I don't exactly encourage my players to take it in most games, but I've allowed it before. One of my PCs right now is in the Red Dragonarmy (Dragonlance setting) and has Draconic Leadership for a juvenile red dragon, which makes him unbelievably happy. Since the dragon's saved the party from a TPK twice in 2 sessions already, the players have all agreed that it's a good thing he swapped out weapon focus (bastard sword) for it =P
Before that he had a 10-headed hydra, which while not exactly unbalanced, took way too goddamn long to resolve 10 attacks at a crummy attack bonus each round.
I've also strongly encouraged my PCs to take leadership in a game where they are all various Cormyrean nobility (Birthright in Faerun game). The last 2 sessions I ran were actually "cohort+followers" sessions where the normal PCs stayed at home while their cohorts adventured, weirdly enough.
So yeah - as a DM, I like Leadership as a way to shore up a small party and help with roleplaying. As a PC, it would be either for a decent mount at higher levels as a martial character, or to shore up a typical gap in the party (crafting, healing, trap-finding, etc).