There are a bunch of us out there that ride in the snow with regular mountain bikes. Mind you we haven't had any snow here this year (okay, 4 inches for about a week...) so I haven't ridden in any this year
. I lived at much higher elevation for many years, and rode all winter every winter (-35C, and up to about 10 inches of snow were my personal comfort limits). There is a mailing list for "Icebikers" (mostly commuters), but there are a few hardcore trail riders (even in Alaska). Check out
http://icebike.org/ . There is a link to the mailing list from there.
I think the general consensus is that these track conversions are too hard to pedal to travel any distance on them. There are wide rims and tires available for the snow (search for Snow Cat rims-double normal width) that work much better.They were developed to race in the Iditasport 160mile winter bicycle race.
For my riding (I only ride for fun) I prefer to use a wide/soft mud tire, lower the pressure a bit and stick to packed trails. Snowmobile tracks are great to ride on.
Nice to see some other crazies on here!
Dean