I change at work, but not because of the ride (3 miles, mostly downhill), but because of the hour-and-a-half train ride at the end. I wind up rumpled and dishevelled crammed into those little seats for that long. Also, when it rains, it's nice to have some dry pants.

Mostly I bring in my clothes on Sundays, when the trains don't run and I have to drive in. If I have a sunday off, I use a pair of 15" Eagle Creek Pack-It folders. I can bring in two pairs of pants and a shirt, or two shirts and a pair of pants, and they arrive mostly wrinkle-free, and I have clothes for the week (I have a (very) small closet in my cube).

Both folders can fit into my Detours Uptown pannier, along with a change of socks. The Jandd Commuter pannier can fit a few 18" Pack-It folders, and the Caradice Bike Bureau and North St. Woodward can each hold a pair of 15" folders - these turn easily into off-the-bike bags, which might be a concern if you have a bus ride, train ride, or long walk as part of your commute, where the Uptown is more of a bike-only kind of pannier.

I can't stand wearing a messenger bag or backpack on a bike. For those of you who claim it doesn't move around on you or toss you off balance, god bless you, because you're way more talented and/or lucky than I've ever been. The pannier's been a godsend, and the reason why I still commute year 'round.