Originally Posted by
sudo bike
I run 35's and don't feel much practical difference between that and 28's (and no difference in commute times at all), at least in terms of speed. It is, however, noticeably more comfortable, and I can generally run over rocks and other debris without fear of falling. Buddies running sub 28's go down hitting a decent sized rock, I don't even pay attention since it just doesn't matter.
I switched from 37s to 28s about a year ago, and, as you said, the rocks are still not a safety problem at that width, but I have noticed an odd little phenomenon with the less-fat tires: when I ride over rocks in the road with the 28s, they often shoot out to the side at very high speeds, and sometimes hit parked cars.