Excellent Bag, Great Fit
For starters, I'm a bigger guy, wide shoulders, overweight, the whole package, so usually I find mummy bags pretty claustrophobic, but the AlpinLite fits pretty well, it's not so tight that I can't move, but it's not so cavernous that it looses its function as a mummy bag.
I took this bag with me to the Grand Canyon in Nov '09, and while the night time temps dropped pretty low, down into the 40s or 30s, I was so toasty I had to open the bag up a little until fairly early in the morning. The weather was nice so I just set up on a picnic table and slept under the stars, no issues with condensation or anything.
I'm looking to do some winter camping next, I think due to the continuous baffles, I can probably shove some of the down from the bottom around to the top and maybe get a little extra loft, so we'll see how that goes.