I spend on average about 4 to 6 hours per day with about 8 to 12 hours on my "weekends"... So about 180 hours a month.
And I don't play any other online games. I have tried a few but they all pale in comparison. I keep wanting what UO has. Other games are an ok distraction... but eventually I want the sense of community I get from UO, the ability to own and design my own piece of the land... the customization of UO, the variety of how many different characters I can play, the RP... and the EM events. Most other games just fall short of the mark when it comes to the scope of UO. Granted many of them have pretty graphics and all... Pretty pictures do not make the game. Even they get boring after awhile. And yes even UO does at times get boring... but usually I have too many things going on to stay bored for long or some friend will come by needing help or something and it'll be fun all over again.