Google introduced the Canonical tag a while back now. It basically is a 301 redirect, but without redirecting individual users. We know it has yet to be supported on Bing or Yahoo, but Google supports it and they even support cross domain canonical instructions.
A WebmasterWorld thread has some SEOs discussing how effective it is. Some say it is really slow but ultimately works, some say it is very fast and works well. What do you say?
How well does the canonical tag work on Google?
Forum discussion at WebmasterWorld.