1) Zealots -- They consider debian the only solution.
2) Lack of enterprise support -- FAI (fully automated install) is debians attempt at what RedHat's Kickstart kicks ass at. An easy way to image/build many machines very quickly. Besides this debian-stable's software is comonly too stale, while debian-unstable, well, is completely unstable. Debian-testing, might be the best, but there is no way to pick a date and keep only the critical things you need. Sure Redhat can be a PITA but at least it supports it's distros fully.
3) Support -- (lack there of) -- The people i talked to on IRC consider anyone that has any problems as a "newb" and that they obviously must be an idiot.
4) apt-get is cool -- (damn, this was a why debian sucks list, but its not all suckage.)
5) Packages are modified -- Debian has a habbit of taking packages like Apache HTTPD and completely changing its defaults, and adding their own patches, while this may seem good at first, it makes pinning down problems and mis-configration more difficult.
Well. Thats good enough for now.