grantm,
There is a better reason to use $0 then leaving the filesystem littered with lock files. I pointed out to Nitrox here that in Unix, it is possible to delete a locked file, and that he should use the process table or semaphores instead. He wanted to know if there was a way around this, and I replied with this, which is an attempt at security through obscurity.

What Dominus is doing is beautiful. By locking $0, it can't be deleted - or rather it can be, but then there wouldn't be a program to run Dominus++.

Cheers - L~R