I have a different approach. I try to keep my load fairly light -- that is, what will fit in a Carradice Barley seatbag -- most of the time. I restock bulky and heavy items (bath towel, slacks, spare shirts, extra food for the office, etc.) on days that I drive, which usually works out to one day a week, and also take home dirty laundry. I keep a pair of shoes at the office along with extra clothes, towel, bath supplies, etc. My daily load usually consists of a shirt, t-shirt, underwear, wallet, lunch, tools, spare tube and repair kit, small cable lock, spare batteries. All of this easily fits in a Barley bag with room to spare. On sunny days with no rain in the forecast, I often ride one of my fenderless bikes with even lighter loads.

On rare occasions, I ride my touring bike with rear panniers, just for the "fun" of it. However, I don't understand why someone would choose to ride with panniers every day unless they had no other options. It just seems like you would be lugging around a lot of extra weight and creating a lot of wind resistance, and my 30+ mile commute is enough work already.