After having dinner at someone's house, is it ok to write a "Thank you" note per email?

That would depend on how formal the relationship is. The more formal it is, the more you should consider "snail mail". If it is less formal, and the invitation came through email, I would think you could send thanks through email. These are uncharted waters in this modern world, so the above is simply my opinion. I personally save all personal correspondence in my email, but do NOT do so with snail mail small things like thank you notes, if that holds any bearing on your decision.

It would be so impersonal to go by email IF THE OTHER PERSON was materialistic! Email is 100% safe. Hell, it's the way of the future. Save a tree right? LOL. Anyway, yes email is just as good. If your dinner host gets upset that you didn't send it on paper instead, they are materialistic and immature. A thanks should be appreciated not matter how it is given.

email is o.k. if they are a computer person.

You send a written note to the hosts' home. An email is too informal.

i think it depends on the person... if its a girlfriends parents, then i think a papernote is way better than an email.. if its a first time date.. a cute email is sooo sufficient.. make sure u add color to it if u can... if its a girlfriend, an invite to ur place for the next one is great.. and if its a guys parents... u should have bought a gift to them to begin with... it depends a lot on the age... but i think that a phone call if u basically know the person is sufficent... and i think that an email if its someone u know very welly and they are of the same age as u... member to always respect ur elders... so the older they are, the better the thank you should be...

A paper card takes more effort and seems a bit more sincere...but email is better than nothing.

I think that the best way is to say it "face to face",no paper,no e-mail

I think it really depends on the type of person your host is. The goal of etiquette is putting the other person at ease, so I believe that true etiquette takes into consideration the type of person you are interacting with, their values and comfort ranges. A younger generation (up to the age of 50 ish), laid back person who regularly communicates by email & who isn't very focused on the traditional details of etiquette in their own personal life will be impressed by a thank you via email. This is the person who sends e-cards for their friends birthdays / other occasions, and who did NOT send you a printed invitation to a formal dinner - but perhaps made the invitation by phone or email. This person would find a paper "thank you", sent by mail, to be far too formal and might be a little uncomfortable receiving it. An older generation (55 or older) person who enjoys hosting a more formal dinner (which you would be expected to dress up for & who sent a printed invitation to you) and following traditional etiquette rules would be dissapointed by an email "thank you" and would really enjoy receiving a paper "thank you" sent by mail.

It would be more appropriate to send a card in the mail.