Does meaningful commenting on blogs and articles with relevant keywords improve the search engine ranking ?

In addition to what said, I would add that while this is a viable option for creating backlinks I'd temper expectations for am immediate "lift."  You seem to have a sense of urgency and commenting may not provide the SEO rocket fuel you're looking for. Are you verified in Webmaster Tools?  Submitted a sitemap?  Pinging the search engines via Feedburner? Depending on the competitive nature of the terms you're targeting, you could see immediate traction by finding a niche where you can be a first or early mover on a topic.  Be sure the content is  original and even if it has been covered before, make sure your title tag is better than the competition.  I often see high visibility sites get lazy in their title tags because they know they can drive traffic without SEO.  Also, be sure to have original images that are well optimized.  Use keywords in the file name and alt tag, surround it with text and avoid using photos found elsewhere on the web, Google Image Search also attempts to filter out duplicate content. Since Caffeine, Google is trying to bubble up quality content regardless of how large the site, PageRank or age so this can work in your favor. Directories like DMOZ and Yahoo are very valuable but may not accept sites that are new. There are other quality peripheral directories but you may want to avoid submitting to too many that easy are low hanging fruit. Time is better spent elsewhere. Hope this helps

If you are just going to repost the same comment on a number of sites, not only will that probably have little value in terms of SEO (as many people suggest, many blogs have no follow tags) but you will build a reputation in your community as a spammer. Rather I'd suggest you develop a strategy of building relationships with bloggers, commenting on their blogs on a regular basis, and connecting with them through social media. You want to get to the point where they are reading your content, and referencing the content on their own blogs. It's a long and time consuming process, but the results can be really great in the long term, and that's why you commit to following such a strategy

In short, yes, meaningful commenting on blogs can help your SEO, but you have to do it right. Do not use the name "Cheap discount replica watches for sale" when you leave a comment on someone's blog. Just use your real name, or maybe use your brand name. Just don't use your keyword. Try to comment on blogs relevant to what you do. If you are reading about space exploration, then seeing a comment from StubHub might look a bit odd. Commenting on articles isn't all that effective, at least I have found. However, writing the articles and getting relevant links in them can be very effective. Checkout http://articlesdirectories.com for a good list of article sites you could submit to. Don't forget to add your site to quality directories as well. These tactics are all good ways to improve your pagerank and rankings.

Unfortunately, most likely this won't help much. More often than not, any links in blog comments are nofollow-ed and won't add to your PageRank (which shouldn't be used as a success metric anyways). Plus you're likely to aggravate people by "inserting" your "meaningful" business description all over the place. If you need quick traffic in the short-term, I'd recommend spending a little money on SEM.

Not sure if and how you can do it, but a viral social media conversation can drive some immediate traffic to your website from different geo-locations and can increase search activity related to your content. This will help you get some boost. Blog commenting on high PR DoFollow blogs will get googlebots to crawl your website more often. Combined this with the above technique, will surely get you some PR. The only challenge is creating a viral conversation, which not many have been able to achieve so far. This might help : http://www.livemint.com/2011/12/08003854/How-8216Kolaveri-Di8217.html

Yes when you leave meaningful comments on blogs, you can build great relation with that community. By placing sensible remarks, you website can easily attract lot of visitors. The readers can also recognize you as an expert which in turn will help you to improve your search engine ranking.

I think I probably disagree with the others here. If your comments are on relevant blogs, then they will help. The amount of "Help" is vastly larger with DO-FOLLOW links, which are much harder to find. Also, it would not be smart to ONLY do this activity for link-building, it doesn't look that natural. Best to do this in moderation, with honestly helpful responses, in addition to as much other buzz creation as possible. I find in concert with other activities (as those mentioned above), blog comments are nice addition to a well-rounded link-building campaign (again stressing relevant blogs and REAL honest comments that help the discussion along).