Another weak spot is the attachment of the bottom bracket shell to the frame, which also cracks on a regular basis. Although these bikes may look quite nice, I'm afraid they're just a big laugh. Actually, there's also a "folding bicycle world championship over here, where a lot of people use try to run hilarious races on them...
Have a look at this advertisement spot:
http://www.youtube.com/watch?v=ufEI1KQrJ_Y