i've shot will all kinds of canon SLRs over the years... 1DmkII, 5D, 7D, and used many of their lenses, up to a 600mm. but generally speaking, the SLRs are just too heavy, and too much camera for the backcountry.
about 2 years ago I was an early adopter of panasonic's m4/3 cameras, picking up a GF1. i now have a gf1, and a gh2, and most of the panasonic lenses. this kit is very versatile, allows me to carry less than a pound (gf1 with 14mm pancake) if i desire, or i can carry the gh2 with 7-14, 14-45, and 45-200 and cover huge focal lengths.
so far, it's the best compromise for me. admittedly, photo quality is not as good as the canon SLRs, but i find it sufficient.
lots of trips and photos i've taken with m4/3 can be found on my blog, if you are curious. www.danransom.com/TripReports