It's probably not required if you're seeking just-another-job from just-another-hiring-manager.

However it's probably a good idea if you're interviewing a founder (especially of a client-based business) who's seeking people who share at least some non-zero fraction of their passion for the business.

I wouldn't suggest faking enthusiasm. But if you genuinely feel like it would be one of the best places for you to work, and you made that clear during the interview, it doesn't hurt to follow-up and say it again.

EDIT: The original "who the f--- writes thank you notes?!" comment was deleted while I typed this.

Thanks for the insight nonetheless.

It was common advice that "everyone" gave when I was in college. I've never liked it as interviewer, so I've never done it as an interview-ee.

What is wrong with making an effort to get a job you want?

Considering the situation, doesn't it always seem more like trying to suck up than genuine?

Sounds like an issue of pride.