I was reading about this last night and it seems a bit shit to me.
Unless someone gets >50% of the vote on first preference alone (thereby winning) only the TWO candidates with the most 1st preference votes are considered.
At that point all the second preference votes for those two are added to their scores.
Does this seem a bit retarded to anyone else? We clearly (depressingly?) live in a two-party country still so barring Ken or Boris somehow making themselves dead/unelectable last minute, that means those two candidates will be for Labour and the Conservatives.
So essentially if you're voting for London Mayor and you vote for anything other than Labour or Conservative with either vote, it has absolutely no bearing on things.
And the result is probably going to come down to whether the Lib Dem voters are at heart Labour or Conservative types.
Why bother with all this second preference shit? Just have the usual 1st past the post crap?