I'll fourth or fifth or whatever we're up to now the Downtube motion. I originally looked a Dahon, but the local dealer didn't think it would work with my size (6'4", 250 at the time, down to 230 now). He didn't have one to test-ride, but I was outside the parameters on the order form. On my own, I found Downtube and ordered a full-suspension nine-speed (I wanted the rigid bike with Sturmey Archer hub, but after I e-mailed Yan he convinced me that it was iffy for my height). I've ridden it 100 or so miles in about a month (I have three other bikes, so the folder gets only occasional use), and the only complaint I have is that the height range is slightly exaggerated. I'd like another inch in the seatpost, but it's certainly rideable as it is, though I did put on a longer stem to increase the reach to the bars. I've done a couple of my shorter regular training rides (15-22 miles) on it, and the time isn't far off what I do on my Atlantis or Rambouillet.
One caveat: You can order direct from Downtube for list price, but the company also sells on ebay and they're often cheaper there. Same source, same shipping, same warranty, but I've seen them go for $75 less than I paid.