When I still lived in Anaheim it was once or twice a month. However, since having to move to Arizona I can only afford to and get the time to, get over there once a year. I took it for granted living so close before, it kills me to only get over there once a year now.
I live about 24 hours away from Disneyland which makes it a little tricky to get there as often as I would like without spending a small fortune on flights. We've been twice in the last 3 years and I think I've convinced my wife to go every two years now, as long as the funds are there.
If it were up to me we would be going once a year and what I would really love to do is move to Southern California and get Annual Passes and go once or twice a month.
We've gone every year for the last 10 years but we're taking a good long break.
I've had it with the higher prices, long lines but mostly, it's the severely declining maintenance I see around the park. I'm talking about peeling paint, burned out lights, etc. but mostly it's the filth I see everywhere.
I go once a month or so when my pass is not blocked out. Over Halloween time I usually do one or two extra trips, so it averages out to about 10 visits a year. I have an AP but I also live three hours away by mass transit, so I can't just pop in whenever I'd like.