How do you know when it's time to upgrade your bike? There seem to have been quite a few threads lately about people contemplating buying new bikes or actually taking the plunge.

When does bike envy end and the need to upgrade to improve your cycling begin? Right now I ride a 2007 Trek 1000 wsd, which is my first road bike. I've been torturing myself lately looking at nicer bikes, which is really terrible because I am in no position financially to get a new bike (about to graduate law school! ) so really, why am I doing it? I suppose it's kind of fun to imagine that there will be a day in the future when I can get my dream bike.

Anyway, I'm just curious as to when other people have decided to upgrade.