I assume you're referring to the rear DO's right? I like vertical, but I like to climb a
lot of hills.
In order for them to work right, however, the frame builder has to be sure the frame is perfectly
symetrical and properly aligned or the wheels will not track straight, Which is why you usually only
find them on better built frames, because of the amount of precision needed (I said usually, it's
not a guarantee).
The advantages are that you don't have to align the wheel every time you put it into the frame, and
it won't get pulled ajar if you stomp down hard on the pedals and your QR isn't quite tight enough
to hold up against the added force.
May you have the wind at your back. And a really low gear for the hills! Chris
Chris'Z Corner "The Website for the Common Bicyclist":
http://www.geocities.com/czcorner