Google announced a few months back that they started supporting canonical urls. This is a great feature that we already adopted in a couple of sites (mostly to keep tracking codes from messing with our search engine results.
Unfortunelty, altough Microsoft announced they will support this feature in Live, this was not yet implemented in Bing as of now (Jun 2009).
Nutch, on the other hand, had this on thier TODO list for 1.1.
Also, Google Search Appliance (GSA), is currently assumed by all to not support this (although nobody really knows if it does).
More about canonical URLs: