My 2c on the Downtube vs Dahon thing....I find the Downtubes to be much more ergonomic when it comes to folding:
-The latches on Dahon's are really finicky with extra plastic bits that break (I actually broke the latch on a Curve D3 while folding it in the store). The chinese Downtube hinges are a much simpler and more robust design.
-Most Downtubes have a stand under the bottom bracket (sometimes people call it a "hanger"), which keeps the bike from toppling over while folded. For a folder, this is much more useful than a kick stand because most likely whenever you're not riding it you'll have it folded (although Downtubes also come with kick stands). Dahon's don't have this.
-Dahon handlebars fold between the wheels, which make the bike a real hassle to roll while folded. Downtube's don't do this and, as a result, are much easier to roll around while folded, a very important feature when transporting 20+ pounds of metal.
I paid $300 + shipping for my used 2006 Downtube VIIIH and I've been happy with my purchase...although I'll admit that the bike is noticably lower quality than my Carryme. However, Yan keeps saying the 2008 lineup is much higher quality than previous years and my impression is that he is pretty honest, if not a tad overly optimistic at times.