Hey if you guys are like Compiz, and those guys are like Beryl, maybe you'll both do cool stuff then merge back later after a big kiss and making up session (which I don't want to videotape, thanks)... with a project far more advanced than it ever could have been until someone shook up things.
Oftentimes, a fork like this just makes everyone realize that communication sucked on account of all parties, and usually a few things happen after this (in order of most common to most rare):
1) BOTH projects die because they are spread too thin.
2) One project survives, the others go cry in a corner (see xXorg vs. X-free86)
3) Both projects do very well standalone (see just about any Linux distro)
4) Both projects do well, realize they are wasting time duplicating effort and then they get humble and merge back together (see Beryl and Compiz).
My examples come from the OSS world.
Read all about them on da Google. Frankly, what's going on with them, and their histories, is amazing, and QUITE the lesson for people trying to work on shared projects.
The experience of others can teach you what to do and what NOT to do.
Regardless how this turns out (let's cross our fingers that we can cross off #1 at the very least shall we?) GOOD LUCK!