I, uh...
ahem...
I've LARPed. I went to the original NERO center in western Mass. for a few years and always had fun... of course, I always was an NPC, and only showed up to play at night. They give you a goblin/skull mask, stats, a weapon, and some "gold". You give a piece of the gold to whoever kills you, then walk away and re-gen a few minutes later.
Fun:
Running around at night in a mock-medieval village, acting like a goblin, screaming, occasionally ambushing a party, RARELY killing a PC, and sometimes even getting a powerful monster (I once played a Death Knight).
Not fun:
The players travel in groups of twenty. You and your monster buddies are maybe three or four strong. The PCs thwock you with their weapons as hard and as fast as they can. I normally just went down as soon as I entered combat, so that I could avoid the beat-down. Most times it didn't help.
I always liked it, and have been entertaining the idea of going back to join the hated enemy: the PCs.