Rich Zygler warns employers against a certain type of PHP developer that lives out there - the "Lone Wolf":
I've run into the Lone Wolf PHP Developer at several places I have done work. Sometimes, I've had to work side-by-side with the Lone Wolf. Other times, I've replaced the Lone Wolf who had moved on to different hunting grounds. Still other times I've had to hire people and had to choose between a Lone Wolf and several other candidates.
He lists out a sort of checklist to see if the person you're working with (or you!) fit into the "Lone Wolf" mentality. Things like not working well with a team, does work on production servers, never reads blogs or keeps up with the community and has a habit of coming up with overly complex solutions for simple problems that might not scale all that well.
Check out the rest of his list for more criteria - chances are there's already a "Wolf" prowling around in your neck of the woods too.