TOPIC: Thanks??

I learn that when people say "Thanks for nothing",it means something negative. Is that true? How about the following phrases? Are they positive or negative in meaning?
1. Thanks a lot for supporting me.
2. Thanks a lot.
3. Thanks a million.
Thanks,(a real one!)

Thank you for asking about the REAL meaning of "Thanks".
Yes, you are right:"Thanks for nothing" does mean something negative and it is something you may think more often than say (because it would be rather rude) because someone has promised something but failed to keep their promise.
All the following phrases are positive in meaning:
1. Thanks a lot for supporting me.
2. Thanks a lot.
3. Thanks a million.