Since there's renewed interest in fixing the blocking problems (and bug 550), I thought I'd draw attention to http://meta.wikimedia.org/wiki/User:Robchurch/Blocking_Mechanism/Notes which is a proposal for a fresh blocking mechanism.
I suspect this ties in a lot with the other current thread on this on wikitech-l, and no doubt the principles are identical or near as damnit. The precise implementation details are going to differ, but I expect we can bang our heads together and whack out some code soon enough.
Rob Church