I joined my Sunday group in June of last year. Since then, we have played, in no particular order:
-RIFTS (two different GMs/campaigns)
-Rebel Worlds (A homebrewed version of Traveller with some Savage Worlds, RIFTS, and even Star Wars thrown in)
-Deadlands (two legs of a campaign, with a third leg starting up in a couple weeks)
-Stars Without Number
-Two different AD&D campaigns (with different DMs)
-Shadowrun (4th edition, then converted to 2nd edition)
...that's eight different campaigns in the space of about 16 months, meaning each game gets around two months in the sun before it gets shelved. We are typically playing two campaigns at the same time, alternating them every Sunday.
I enjoy the variety, but I miss the stability of running or playing in something that goes on for awhile. Deadlands is the closest thing I've got right now; the game has probably run for the longest length of time of anything we've done with the Sunday group, though the sections of the campaign haven't run consecutively. It's supposed to start up again at the end of the month, replacing Mindy's AD&D game. Also, I think Mindy is planning on starting up some classic Traveller next time she is in the driver's seat, rather than continuing this current game.
I've bowed out of the Sunday group GM's chair (my "time in the mill", as the group calls it) until summer vacation; I just don't have the time/energy/sanity to run a second game right now.