I am. And I'm using the Xtracycle to transport used Starbuck's coffee grounds back home for use in the compost pile. No photos available, but my four year old and I headed to downtown Berkeley last Friday to get a copy of her birth certificate (for school), have lunch, get some groceries and see how many bags of used coffee grounds we could pick up. Check my gardening blog if you care about growing your own and getting free fertilizer to do so.
As this is a cycling blog, I'll tell you that we ended up carrying home four bags of grounds probably totaling 40+ pounds, a bag of groceries and ourselves. The 700' of climbing to get home was a bit rough with a full load, but certainly good exercise. My daughter has also decided to ditch the peapod and just sit on the snap-deck, so that's pretty neat.
Update: Everyone likes photos, so here is one of the maiden coffee ground voyage. Do be careful of leaks, so use heavy garbage bags to protect your bike and panniers.