Thanks everyone for all your responses. It appears that there are four areas of concern

1) frame hinge
2) handlebar hinge/latch
3) proprietary parts
4) seatpost slipage

1) FRAME HINGE - is this just a matter of tightening the thumbscrew so when you close the latch it closes tighter? I don't quite understand why this is being cited as a particular Dahon problem - I mean, don't all latches work the same way (eg. the latch that I open and close to raise and lower the seat on my Brompton). This latch on my Brompton hasn't required tigthtening after 2 months of use, and I think if it ever did it would be obvious because the latch would feel loose when I closed the latch. I would think all such latches would have the same tendency to go loose over time and tightening the thumbscrew is so easy I would not consider it a problem unless it happened with great frequency. Why is the Dahon especially problematic?

2) HANDLEBAR HINGE/LATCH - If I couldn't stand up on my Brompton pedals and pull up or put weight on my handlebars I think I would consider that a serious limitation. Again, is the latch on the Dahon designed differently from others?

3) PROPRIETARY PARTS - I'll put that on my "to consider" list. From what I've read the Xootr Swift does not use a lot of proprietary parts - something we'll take into account when we test ride it.

4) SEATPOST SLIPAGE - This worries me, too. It seems some (most?) avoid/fix this by simply tightening the latch, but apparently others have had no luck fixing this problem. If it is unfixable would that be covered by warranty? I would consider that a serious flaw and would want a replacement bike if it truly could not be cured by simple latch tightening.