recent interview with Gamasutra. The lead designer of Ultima Online says the game is still going strong.
Ultima Online has "got a very core player base, and not a small one", says Cotten. A good MMO will earn player loyalty no matter how long it's around, and Ultima Online is still enjoying that player base after twelve years. They recently invited former players to return for a couple of free weeks, and new content is still a feature -- the eighth expansion was just released in September. Cotten hints at lots more to come too: "UO itself, if you want to go for a historical timeline, we're only around Ultima VI; we've got tons more of content left to play with."
It looks like there's definitely something to be said for old favorites. Keep it up, UO!