As a little update to an older post on this subject, and although this post from Matthew Ahrens is about the new scrub code recently introduced in OpenSolaris build 94--and was in fact a priority before the launch of the Sun Storage 7000 Unified Storage Systems (a.k.a. Amber Road)--it is interesting to note that some of the new code will be usable to remove a disk from a ZFS pool.
As Matthew wrote:
This work lays a bunch of infrastructure that will be used by the upcoming device removal feature.