Hi Tom,
Are you referring to taper roller bearings or double row angular contact ball bearings? I've seen both types used in automotive wheel applications.
There should be nothing wrong with either type, if you understand how to mount them properly. The tapered roller type requires a preload applied either by a nut, or else super-accurate shimming of the bearings inside a captive housing.
If you build a proper preload system, you can be guaranteed that you won't have to settle for any backlash to the same degree as you get from using a single row ball bearing used as a thrust bearing. Standard ball bearings have quite a lot of endplay when the thrust direction is reversed.
Edit: on second thought, see this thread:
http://www.cnczone.com/showthread.php?threadid=1117&s=