A simple "thanks" can go a long way to making an online interaction that little bit smoother.
I've started posting the odd review of various venues on TripAdvisor and one of the things that's really fascinated and impressed me is their emails.
Every time you post a review you get a nice little "thank you" email.
It's not complicated. It's not tacky, but, to me at least, it's pretty effective:
What do you think?