Great, now we've heard from the guy who hates Missoula, and the guy who hates CasperMike.
Having lived in both towns (although Bozeman was almost 20 years ago, before it exploded), there are some major differences. They are definitely different places for those of us within the state. To outsiders they may not seem so dramatically different, but it depends on what you pay attention to.
Bozeman, fortunately most of my good friends from college still live there, so I'm not completely in the dark. The bozone has a "fun hog" scene, many many people out recreating. It is defintely the more urbanified Boulderish of the two towns. Lots of money (especially younger adults) has moved into the area, and many of those people play hard. So while there are tons of recreational options, they are a bit more crowded. Not a lot, but more so. Bozeman is majorly sprawled, but the core of town has a pretty decent sense of small town community. It's got an artsy side to it also. The skiing is great, but Bridger is packed and the steep pitches are over very quickly, kind of like Alta. Lots of hiking and traversing flats. Some people seem to like Big Sky, I find it lacking and trying too hard. Kind of like the dork who bought all the gear, but can't really use it. Moonlight has opened up a huge new aspect to the Lone Mountain scene, assuming they are able to keep it going. I never boated when I lived in Bozeman, and have only run Beartrap on the Madison, so I can't say for sure. Bozeman's got a much bigger valley and adjacent valleys, so it's easier to get a bit out of town and find "cheaper property" (not paradise valley or Gallatin). Missoula's pretty boxed in and there aren't really big open valleys nearby with the exception of the Bitterroot and the Mission valley, neither of which are cheap. You have to go further to find cheaper property in Missoula, but I think property here starts cheaper so it's all relative. Bozeman is colder and snowier in town, not so good for growing tomatoes.
Missoula is much more urbanified, and many say it's a big Boulder but the people with money aren't here. It is extremely progressive/hippie and community oriented, and for the arts it's about the best in Montana. Three farmers markets, at least. Keep in mind UM is the liberal arts school (read party school), and Bozeman is the engineering school (still plenty of good partying that I can attest to). Missoula is much more laid back, and the harder-core recreation isn't anywhere near as crowded as Bozeman. Go to walk your dog and it will be packed. Go backcountry skiing and it's easy to avoid the crowd. Missoula's boating is awesome. Unbeatable roadside 30 mile long Lochsa river 1.5 hours away. Easy to hitchhike shuttles, or just hook up with people to run with at Fish Creek. Also good Class II Blackfoot (maybe some III at high water) which gets some good longer wave trains. The Alberton gorge is Class III with maybe 1 IV at high water. The Blackfoot gets too low by early/mid July, and then the Gorge becomes a complete junk show. High water Gorge is a blast, but I can't imagine choosing that vs going to the lovely Lochsa. There is also the lower Flathead which is dam controlled, but only one real rapid and it's pretty huge. More stuff up around Glacier also. Many more things if you are a fisher-person. Lots of forested lake recreating within an hour also, either north or North-east. There's also a decent creeking scene here. Again, because of the smaller groups of people doing it you'll have to work harder to find it and break in. Missoula is much more mild, spring comes sooner and leaves later, not as cold. Better for gardening. We don't always have snow in town throughout the winter. Foggy/cloudy/inversions can get really old in the winter.
Right now people still think their property is extremely valuable. I bet a nickel that within a year or two people will be back to taking $100K for 20 acres that is too far from town for most to commute.
Montana boating forums? No. TGR is weak in my opinion, I never really encountered anything regionally useful and got bored with the scene. Idaho Whitewater (yahoo) is good for rafting, and there's also a club in Spokane (northwest whitewater association) who has another yahoo group that is very inactive, but mostly used for club activities and hooking up for boating trips.
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye