Google code jam is just a competition where u can tell Google you are there and you can do good programming and yes probably get hired by them !!
And after leaving college and coming to the Industry, the first thing I learnt is that the kind of programming you are expected to do in an organisation is so different than the style we follow in the colleges or promoted by the coding competitions.
Yes, once you submit, you get back WRONG. You question your algorithm, you question your understanding of the problem, you question yourself, you question the forum, but there is no error. Great. So you can just stop trying to solve the problem and do something else and probably assume that either the problem description is wrong or the input/output is wrong. This is certainly not fun at all.
Most of what you learn from programming competitions is not transferrable to business programming, but possibly some is. Maybe you'll see a case at work where dynamic programming might be super-awesome. Maybe you won't, but either way it's not going to hurt. There are be opportunity costs of course (i.e, because you're not spending your time elsewhere), but only you can judge that.
My motto, if I had one, would be that learning is not a zero-sum game. Programming competitions are a form of deliberate practice not unlike cross-training for athletes.
Not that frequently updated, but some really cool stuff there