Having actually used PBS i have to say that it's really powerful.
Verifying all dependencies including CFLAGS is something i really miss at work, since it would save me from a lot of grief, and it's something no other build system i have played with has done.
While any advanced and sufficiently powerful system might seem hard to grasp for the beginner, it's usually worth it in the end.
As for the other comments left here, i wonder...
Not portable? It's PERL!
Problems with the license? Thats the authors discretion.