I tend to wear a small backpack for commuting since I don't like to have a rack and panniers moving about and making rattling noises. Bought a Dahon Curve D3 in the fall. It came with a rear rack, which I removed. It also came with a Tern front truss and bag (this one http://ep.yimg.com/ay/nycewheels/dah...ing-bags-4.png) which neither I nor the previous owner could remove from the bike, so he threw it in. I thought it was ridiculous and too small... it is about the size of a tiny cooler or a very large lunch kit. I was able to squeeze my work clothes into it for my commute and I rather like it because
- no rattling noises
- very secure, but quick to remove
- the weight is very low on the bike
- my back doesn't get sweaty in the summer

I have to say that I thought it would throw the handling of the bike off, but it doesn't.