Please note that the single user login account merging system is up and running in a live demo state since Wikimania at http://test.wikipedia.org/wiki/Special:MergeAccount
One request: Please distinguish between accounts which have matching password/email and accounts that don't match but have no edits so will be merged anyway. The list of accounts it intends to merge with mine includes quite a few which I certainly didn't create, which could be rather confusing (well, to be honest, it *was* rather confusing, I thought it was a bug until I thought to check the contribs and saw they were blank).