Topcoder is fun, although I havn’t done too much on it.
Cool to see google PR $$ landing somewhere good. (as well as summer of code).
Only thing is, programming competitions are a very specialised form of coding, topcoder even more so.
The questions do test general programming skills, which is great, but competition coding is developed to the point where it’s very hard to compete with the specialists.
In other words, I imagine one is unlikely to place in the top 100 by simply being a excellent coder, you’d actually have to be a competition specialist as well.
Still lots of fun :)