SourceForge has by far been the most popular place to host open source project. Freshmeat is one other popular home for open source projects. It's interesting that Google itself is entering this field and offering a place to host open source projects as well.
Sure Google aims to pushing open source to the limits by doing so. I've had a look at Google's open source hosting service and found it to be very clear and clean. It is easy to use and I believe would be so convenient for hosting open source projects. I believe this would give a boost to the open source community. Unlike with SourceForge, you do not have to wait till your project gets approved when hosting it with Google. I remember trying to host an open source project at SourceForge before, when it finally got accepted, I found it extremely difficult to know how to get about performing any sort of actions on their site. I believe the simplicity Google is introducing for open source project hosting would create a positive boom in the open source community helping it expand dramatically.