I'm not sure whether other people find themselves in this situation, but I thought I'd show you my solution, and ask you how you deal with it: how do you carry a folding bike on another bike?
So, I ride my bike to work every morning. I work on a college campus and I don't have a parking permit, so driving a car is not an option. Not infrequently, though, for one reason or another, I don't ride my bike home in the evening (usually because of bad weather -- I commute in dress clothes). I then need a way to get to work in the morning.
I could walk (it's only 1.5 miles), but I'm really not a morning person and the extra 20 minutes are actually pretty valuable to me. I could ride one of my other full-sized bikes, but then I'd have two bikes to ride back. So I recently picked up a Dahon Piccolo, which I can strap to my regular bike and ride home. It's a little ungainly, but it works.
One of the guys at Harris Cyclery showed me a photo of a Brompton strapped to the side of an Extracycle, but I don't really want to spend the money for either one. Do any of you have better systems? Show me what you've done!