This is an interesting topic and lots of diverse opinions voiced. I do agree with one of the comments made that if someone is helping for any sake other than giving back to the community (i.e., helping just to get a "thank you") then that's probably not the best reason to help. A TIA or a subsequent "thanks" is great, but if it doesn't come you should still feel wonderful that you've been able to share some hard-learned knowledge and helped someone out of a jam.

That said, if there are particular people (online or otherwise) that are net consumers of your knowledge in a very unappreciative way, or actually come back and "demand" that you fix up your suggested solution, then the line's been crossed and it's time to let them fend for themselves. Hopefully cases like that are very few and far between.