I must have riled you up or something. If you want to recommend Back Track as an introduction to networking distribution go for it.
Backtrack is awesome. And if anyone using linux can't use it as a first off, they probably shouldn't be playing with linux.
OP: Backtrack is not any more difficult than any other distro and comes preloaded with tons of security tools.
Redhat is a classic.
Ubuntu has a large userbase(making problem solving easier).
Suse/Opensuse is fairly user friendly.
Peppermint is my current distro of choice.