Back in the day before I was a parent I think I played about 5 hour a night and usually about 20 over the weekend.
Now its less than 2 hours a week(It could be more if I could be bothered, I just cant find the enthusiasm at the moment)
There is also the problem of no game has really hooked you like Halo 2 did. I am sure if there was one you would be on the majority of the week. I have a similar problem, but there just hasn't been that one game that hooks me since the Halo 2 scene died.
I am hoping and praying that Bungie make Halo Reach perfect, but I'm not holding my breath.