I just ran into an odd issue with the init script in 3.0.5 built from source running on Ubuntu 6.06 (old I know, but it's LTS). It uses LSB's pidofproc to see if there's already a server running. pidofproc uses the full path to the binary to ensure it's looking at the right one. Since gluster server and client use the same binary (glusterfs is a symlink to glusterfsd), if it's running a client but not a server, it will erroneously return the pid of the client, report that a server instance is already running (though fail to find a pid), and thus prevent the server from starting.
Looking at the docs for pidofproc, it's supposed to fail to return a pid if it doesn't find a pid file; in this case it wasn't returning a pid (there was no pid file for the server or client in /var/run), but for some reason it was still being counted as running. I don't know if this is an Ubuntu problem or just some random weirdness.

I solved it by stopping the client, then the server started ok (suggesting the matching path was the issue), then I remounted the client and it all worked.

This could be fixed by replacing the symlink from glusterfs to glusterfsd with a hard link, or (probably safer) replacing the symlink with a simple script wrapper around glusterfsd. This way the two programs would have real distinct paths and thus avoid the opportunity for conflict.