Let's compare. Google Code Project Hosting (GCPJ) vs SourceForge.net (SF).
You can start using GCPJ in <1 minute. With SF, you have to provide all those tax-forms-like details and wait until your request for the project is approved.
The project front page in GCPJ is cleaner than that in SF. Don't even bother thinking about the old version of SF.
GCPJ's label-based issues tracker is much more usable than the complicated SF's one. Everyone hates a bug tracker anyway, somehow GCPJ is still humanly managaeble.
Often you want to put some information quickly and the GCPJ wiki is fantastic for that. No need to create some web pages, upload them, and so on. Yes there is also the wiki support for SF but how many of you use it or even are aware of it?
The download page in GCPJ is easier for eyes.
Optional goodies are not packed within GCPJ. If you want to display some screenshots, redirect to Picasa Web Album. Need some mailing-lists? Connect the project to Google Groups.
Tracking the statistics (visits, hits, referrers) is easy because it is integrated with Google Analytics, which btw provides more useful information compared to the limited SF's stat tool.
Administering your project in SF can make you scream (aloud!). It's however dead simple in GCPJ.
SF's subversion access is known to be flaky from time to time. GCPJ's might not be the fastest, but so far it works smoothly.
GCPJ's subversion viewer (the very latest feature of GCPJ) is a way way better than SF's traditional one. Try both and prove it yourself.
In short: GCPJ is designed with Pareto Principle in mind. Most of the core features which the open-source developers (who, BTW, do not have so much free time) really need are made very easy to handle. It's rather minimalist, it's not perfect, but it improves over the time. SF is so dull and not for mortals.