When should one introduce advertising to a new website?

It really depends on the purpose of the website... If it is an advertising-led publisher site then do it from day one - because it will help you recognise the relationship between your traffic and advertising revenues. It will help you put some numbers behind your projections and start up those all-important advertiser relationships. If it is a social/usable tool kind of site, then perhaps it is best to delay whilst users start using the service and then you have a decision - ads vs. subscriptions. I would always go for subscriptions first as they're a much more reliable revenue stream, however if that is not possible, then ads are a poor relative. If it has a specific purpose / funnel then it probably needs to focus on the main revenue streams than worry about advertising. Use space for 'internal' advertising (promotions) rather than sending clicks away. Two learning experiences for you: 1. If you are thinking of advertising then make sure you plan the placement of the advertising units. Trust me, you don't want to have an early re-design because you didn't get it right in the first place. You need to particularly cater for MPU (Square) units - as these generate bigger eCPM 2. Get your ad serving right so that you can manage your ad relationships and be able to book ads directly into your site as well as through networks. Structure your site and placements for targeting for advertisers so that you can upsell more

If you can secure advertising that is both site-specific and respects why users come to the underlying site in the first place, I believe advertising is a welcomed addition to almost any site at any stage. If the site is unable to secure site-specific advertising and simply plans to run general ad-network ads (e.g. Google Adsense) then I'm of the opinion that you're better served delaying for as long as possible. Two reasons: 1. General ad-network ads aren't going to make your site look more legitimate, rather it'll make it look like the million's of other sites/blogs running the same generic ads sprayed through networks. 2. General ad-network ads aren't going to deliver significant revenue - with ad-network ad-rates often falling below $0.20eCPM (the amount earned per 1,000 ad-impressions) http://NOTCOT.com is an example of a site with a relatively small audience (50K-100K visitors in the US) that regularly has site-specific advertising, taking an already fantastic site to another level.

If your business model is going to be advertising, you need to introduce it as early as possible. There's a big difference between a product and a business. A business generates revenue and a sustainable business brings in more money than it spends. It takes a business a long time to get good enough to earn a significant amount of money and then it takes longer to make more than you're spending. You need to start that journey as early as possible if you're going to be more than a product. Best of luck!!

Good question. Thought/suggestion/recommendation...It might make sense to base the displaying of ads on the visitor. For example, first time visitors (read: no cookie) don't see any ads, or minimal, or maybe at least not on the first page they land on. Returning visitors might be given a different experience. Within those biz rules maybe there's consideration for source of the traffic. Those coming from Twitter get a different experience than Facebook or Google SERP vs PPC. That said, I'd like to add that if ads are going to be considered the primary source of revenue maybe there are other more appropriate options? For example, if you have a B2C brand maybe you can sell t-shirts and other branded items on Zazzle? Yes, that's much different than just tossing up some ads but it might ultimately be a more effective long term strategy. Maybe?

I think we're missing out another aspect here ( this is touching on your question of how much money can you make from advertising on a freshly launched site): if you do start with advertising on day 1 on your site and you start with some big names in there, you will guarantee that other advertisers will look at your online solution more seriously and as such it will be much easier to hook up with other big advertising budgets! Obviously as it was already suggested here you need to ensure that you do not drive away your users, however, having advertising from day 1 could help and could in fact drive more revenue from advertising. (Think about it like this: if Sony Playstation thinks your site is good enough for them to spend advertising budget on, then you can bet your bottom dollar that Microsoft/XBOX, Nintendo etc will follow!) Also worth bearing in mind the product uptake curve -- the growth in the userbase is normally exponential in the initial period (be it days, months, years) and then it stagnates and decreases. It is during this period you need to sort out your advertising partners -- once the decline starts you will find it more difficult to do that -- and as such, once more, it makes sense sometimes to start with advertising on your site from day 1, and even more, makes not just sense but money as well!

In my opinion, yes, you should wait until you have enough traction otherwise the site will give the feeling of cheap to the visitors. Besides this, how much money can you make if you put ads on a freshly launched site? How enough traction is enough? Well, that depends of the industry you are in. Visitors from one niche may be more valuable than others. Anyway, you should have at least several tens of thousands of visitors a month before introducing advertising (some say that you should start monetizing when you are over 100,000 visitors/month but this is most probably applicable to content websites).

Advertising is typically not a sustainable business model. But if that is your model, keep in mind it basically won't make much money until your impression volume gets quite high. Given that consideration, the negative impact of advertising will likely slow your growth path with virtually zero financial upside, so i would definitely delay it if you have the option to do so...

I would suggest that if your intention is to monetise your website through advertising then you should have advertising on your site sooner rather than later... preferably from day one. As was the case with Twitter and Facebook... people react to change... be it in interface design or advertising (and that reaction is often negative). I would place some form of advertising on your site from day one as it will save you the heartache of people reacting to the change of having advertising... and also the design changes that would need to be done to accomodate advertising down the track. Placing advertising on your site early will also provide other advantages, mainly through what you can learn about your users likes/dislikes on your site... and use those learning's to both adjust your approach to bringing in advertisers in the future (types of advertising) and also your sites content (adjusting if you like towards content that delivers higher eCPM's).

I do understand that this is not your question but before adding any ads to your website I think you should definitely look at other monetization options. You have to keep in mind that every person that click on an ad from your website leave your site and might not come back. Is it worth a few cents? Studies have shown that people mostly click on ads by accident therefore it doesn't really help your brand. You could consider other alternatives such as building an email  list for promoting affiliate products, selling products directly, etc. Otherwise, as other members have stated, it all depends on the type of website that you have developed. Good luck!