But BOINC is more than the server source code. It's also a client-side program, making it possible for a single user to participate in a variety of distributed computing projects with a single application. It's currently in beta.
This makes me really happy. Not only was SETI@Home the most well-known of the various distributed computing projects, it ran on a wide variety of platforms, including some not normally included in other projects, such as the Mac and SPARC. BOINC continues this tradition, running on Windows 95 and up, Linux/x86 (possibly others to come), Solaris/SPARC, and Mac OS X.
Once BOINC is out of beta, we could see a flowering of interesting distributed computing projects. What can be handled with this method? Anything that requires mathematical analysis of lots and lots of components. Current non-SETI distributed computing projects include protein folding and climate prediction.