2 Answers

It's part of the karma system here. Thumbs up is for good answers, ones that answer the question asked in a correct manner. With a thumbs up comes karma points. It's a way for the person who asked the question to thank the person or people who answered it. The points also reflect the level of trust the community has in a  person to give good valid answers. We reserve the thumbs down for really bad answers, like abusive or vulgar answers. We do not give  a thumbs down just because we do not agree with someones opinion unless it is like I said, abusive or vulgar.

I think you also get karma points (or lose them )based on the questions you ask as well as the answers you provide.  I'm going to give you a TU by putting my cursor on the TU under the question you asked and click on it.  You will get 15 karma points and be notified that Bob/PKB has voted up your question.  If you click on the TU by any of the answers given  here (Colleen, Expert, Bob/PKB), watch the number next to "karma" under the responder's name increase.  If you vote the TD, watch the number decrease.  If you "THANK AUTHOR", the karma also increases.  Whenever someone TU or TD your questions or answers, your karma points are affected and you get notified.  Like Colleen said, don't TD someone's question or answer  unless you find it offensive or vulgar. OPINIONS are encouraged.  If you feel the Q or A is seriously unacceptable, you can "Report abuse".