I think they're functionally good vehicles... high quality, lots of room stuffed in a small package and what not. And the xA doesn't look too shabby-- in fact, we were behind one today, and the rear looked remarkably like a Mini Cooper (albeit with large tail lights), the front looks okay, and the sides are semi-aggresive. The xB is a bit too squareish for my tastes, and the wheel-to-body ratio looks really odd.
While they're very good vehicles, I think it'll have a bit of limited appeal in the younger market (notice that I say "limited", not "none"... the first time I saw an xB, a teen was driving it), because let's face it-- kids these days want modded Civics, old Mustangs, or big trucks. They'll sell among Gen Y, but I don't think as much as they'd like.