That whole thing about not liking people from out of state can be true to an extent, especially when newcomers think they know better than the yokels and try and change everything because it's so much better where they are from (why'd you leave then!). But if you try to assimilate, are nice, and forego activism until you have done some time to get a real sense of the place, there isn't a problem. Speaking as an ex-Californian in Idaho.
The Treasure Valley (Boise) has a lot of transplants because of the tech industry so it's not as bad there. In fact, if I recall, Canyon County is the only left-voting county in the state.
Boise is a great spot if you aren't looking for the big city feel. They've got a great downtown area with some culture and dining that is on par with much bigger cities but someone coming from a larger metro area will probably still find it pretty low key and possibly boring. It still gets overlooked by a lot of major entertainment tours but there's a healthy amount of smaller acts and club entertainment. BSU will never be mistaken for a major research university but it's overcoming its image as a commuter school and has taken a lot of the in state students that would have gone to the University of Idaho in the past. Boise is pretty granola friendly so wear your earth-muffin Birkenstocks every chance you get.
If you're the outdoorsy type it's just 2-3 hours from Hells Canyon, Stanley, Sun Valley, Sawtooths, White Clouds, Frank Church Wilderness, etc. Idaho has more wilderness area than any state except Alaska.
Drawbacks? Boise is a little hotter than SLC (I've lived in both), it is a complete desert when you get 15 minutes south or east of the metro area. Traffic is awful, too. There has been a big population boom the last couple of decades and infrastructure hasn't kept up especially between downtown and Nampa. Boise is on an island, too. Once you get outside of Boise, Idaho is pretty rural. Next city you hit is Twin Falls to the East about 115 miles (about 45,000 people) and another 110 miles to East Idaho where there's about a 250-300,000 people. The next substantial city is SLC and that's about a 5 hour drive. The airport is pretty small and getting a direct flight anywhere is not easy with a lot of air traffic connecting in SLC, Seattle or San Francisco.
I don't know how old you are but if I was in my 20's and trying to decide between SLC and Boise I would pick SLC in a heartbeat. It's bigger, busier and just feels like a real city (may be the opposite of what you're looking for). Job options are a little more varied than Boise (which is very tech centric) and there are 5 major universities up and down the Wasatch front. The night life is good and if you stay in the Salt Lake Valley you will avoid the concentration of Mormons in Utah Valley and Davis County. Housing costs are really similar to Boise and there is a lot more going on in the way of entertainment, sports and the winter activity options are the best you will find in North America. There's 7 indoor arenas with seating capacities of 9000+, 5 outdoor stadiums of 20000-68000, 2 or 3 large ampitheaters and several concert halls and art venues within 90 minutes of downtown SLC. I've been to music concerts in both Boise and SLC and SLC draws bigger, more energetic crowds; the exception being Alt Rock which really seems to have a place in Boise. I always felt that SLC was a little more diverse, too. The Mormon influence can be frustrating but it's no worse than Protestants in the South, Catholics in the East, Jews in New York or anywhere else that has a dominant religion. SLC is not a smoggy town. In the winter, you can get inversions where the smog gets trapped in the valley created by the mountains on both sides but it really isn't noticeable more than a handful of days out of the year. The traffic's not great and you still get the rush hour traffic jams coming in and out of SLC but the rail system is pretty good and there was a lot of highway infrastructure put in place for the 2002 Winter Olympics. It's definitely better than Boise which can be nightmare at times.
Last but not least, SLC leads the nation in Breast Augmentations per capita:
http://www.realself.com/blog/salt-lake-city-breast-implants#.VjFp6Suuqjw