I think using the "What's New" link is the best way to keep on top of what's happening on the site.  In fact, it's really one of the best implimentations I've ever used... but I fear it's a feature that just doesn't have a high enough profile for the new or average user to latch onto as quickly as they should.

I also think there should be a message posted at the top of the "What's New" page that tells people that they should join projects to get updates and track activity.  And that joining projects does not mean they have to actually contribute to them... it just means that they are interested in seeing what happens with them.