I'm with the backpackers. I have a short commute and not enough stuff to justify two paniers and I don't like the feeling of the bike loaded with weight on just one side. The only upgrade I might consider is some kind of suspended pack, to keep my back a little less sweaty. I would say that I'm more likely to use paniers in the winter when sweating is no fun and weight on the tires is good for traction.

I do have a rack on my commuter, but I generally only put the paniers on for longer runs.