Don't know Missoula at all, and I haven't been to Boise in five or six years (I like it, just don't know it well), but I live in Reno.
Cycling in the city is like riding anywhere else, mediocre bike lanes, traffic and all. It was a nice, compact place until 8-10 years ago, but the greedheads have taken over, and there's major sprawl now. You used to be able to get out of town in 15 minutes; now it takes 40. Drivers are fairly aware of bikes (there's been an explosion of road riders in the last few years), so that's not a problem, but a lot of local riders have attitude problems, which is creating a growing animosity toward cycling as a whole. It's not really an issue yet, but it's getting there. For what it's worth, I notice that drivers are more likely to yield and be courteous when I'm in mountain bike shorts and T-shirt than when I'm wearing the Full Lance. A team jersey predisposes a lot of people to think you're going to be an a-hole. We can thank one of the local clubs for most of that, I think....
As the city has grown, it's gotten harder to get out of town on a bike, but once you do, the riding is excellent. Donner Summit is 30 miles, Lake Tahoe is less than an hour away, and there are mountain passes (7000-8000 feet) to the north, south and west (east is desert, nice in spring and fall). Pavement and shoulder conditions vary from excellent to downright scary, and we're coming off a very severe winter (worst snows in 85 years), so there's likely to be some damage lingering into summer.
Summer weather will be dry (occasional thunderstorms in July & August), 85-95 in Reno (4500 ft.), 75-85 at 6000-7000 feet in the mountains, but can drop to the 40s or even 30s at night. Humidity is low, so 90 is comfortable riding weather. Nice mornings, often strong west winds in the afternoons. I ride east to work, and it takes me 40-42 minutes to get there. Coming home into the wind can take an hour to 1:10.