I have them on for the fall and winter. They come off sometime later in the spring and stay off during the summer.

That probably explains how I feel about them. They're not perfect at keeping the bike clean but your bike is definitely cleaner with them than without. So during times of the year where it's frequently wet, I have them on, otherwise not. It's really not the cleanliness that concerns me. I just don't want to shorten the life of the components by having them constantly get sprayed with salt and/or grit.

I'll occasionally run into some toe overlap problems with them. The also aren't so great when taking the bike on the train. The racks on the train work in such a way that the bike is standing on it's rear wheel while the front wheel is held about 4 or 5 feet off the ground. It's actually resting partially on the rear fender which deforms it.

Every once in awhile the fenders get knocked out of alignment by something or another and rub the tires. So for me the few wet summer rides I have aren't worth the hassle of leaving them on.