the rack i use at work has a row of upside down U's all welded to a base. seems like that would be convienient cause you wouldnt be able to take it apart but you can still move it around if you need to.
i guess someone with a big pickup truck could come and take the whole thing.
i've seen these newer style racks that look like an elogated Pi symbol, its hard to explain but i guess they are designed so you can set the frame in a little cradle, covered in rubber to prevent scratches, and then easily be able to lock the frame and either front or back wheel with one U-lock. its funny though because every store and restaurant in the area has them but nobody rides there.