I wholheartedly second this motion. Created one myself with Net::LDAP and GTK2/Glade, and I found it about as useful as writing custom forum software. Yeah, you get to control every tiny niggling detail of the implementation, but there's probably something out there that satisfies 98% of your needs (and the other 2% can be worked around).
The one major benefit of the roll-your-own school of thought is that you can simplify for non-techie end users (as inochi implies). That was one of the goals of my system, and it worked well to that end. Not sure how many of the open source solutions cater to this crowd.