I have found myself RPing in games. but not in mmos and maybe not in the tradional sense.
for example I used to love playing pvkii and talking to my teamates via voip in a pirate accent, or viking etc. I liked rp'ing characters in cRPG, at least in terms of equipment/playstyle; ninja, samurai, viking etc. always more fun than only picking best stat items.
RP servers might have more mature communities, but the sort of roleplay intended for RP servers is just fucking stupid and pointless. I realise this is just my opinion but games like pvkii/crpg even singleplayer rpgs have much more interesting capacity for roleplaying than these so called "mmorpg"s.
aye, yon rather stationary gentlemen also doth asketh me to killeth 10eth rats.