An automated thank you note loses a lot of value, it's more of a dismissal, or acknowledging that your problem is solved. Not much appreciation, just slightly better than nothing at all.
Just type a few words of appreciation in the 'Quick Reply' box, send. It makes people feel good, and the time they spend here worthwhile. Also a big plus for you, since not many take the time, you will be remembered for it. Everybody likes to know how things turn out, whether it was a success, or eventually abandoned.
I'm probably on of the worst here. I hop around through several projects at once, seldom get around to find a case for most (yeah, bare circuit boards hooked up every where). I get new ideas all the time, my job doesn't require much thought, but doesn't allow much time to jot down notes. Hard to keep up in my off time. Not to mention looking through boxes of parts, will generally turn up something interesting, pieces start to fall into place, and before I know it, another project is born.