1. It is complicated.
2. It will be expensive; additional layers of complexity always are.
3. It does reward the most "useless" votes/voters the most: you could effectively give multiple votes to a voter intent on the most insane and unelectable of candidate choices.
4. It will lead to more coalitions: this could be viewed as a bad or good thing - in one way endless coalitions mean nothing much can be changed without enormous amounts of horse trading and compromise; however, ultimately the good is that they cannot introduce too many laws straight out of parliament - it will become fast apparent that much of our laws come from the EU which is something a Bory/UKIP caucus is likely to get a referendum on more than a Bory or UKIP minority government.
1. It does require a great deal more focus of the candidate on their electorate; how likely that will last when the whip comes in to play is debateable.
2. It will be more representable of what voters actually want: 3 in 4 voted against New Labour in 1997, likely a government will come in in 2015 that the electorate will grudgingly accept under AV.
Pro 3. I believe weighs out all the cons above.
3. There is now a credible link to a desire for the majority of the electorate to select one candidate: any candidate will need 50% of the total number of voters at least agreeing to their representative; for example, look at Ed Balls fiercely contested 2010 constituency of Morley & Outwood:
Let's assume under AV that UKIP vote for the Bory's as a second, the Watermelons vote for Labour and the Lib Dumbs split between Bory and New Labour and the BNP vote for a single preference; my fag packet calculations indicate that will win and the election will void; where any candidate to pander for secondaries from the BNP will surely result in alienating other voters leading to the same problem.
This has been portrayed as a bad thing, but think about it for a second - the problem lies in the fact that we are presented with candidates who wield absolute power over the electorate and in most cases we wouldn't be willing to pee on them if they were on fire.
We have abrogated responsibility for our lives to incompetents and fools and wonder why things are going wrong - the least we can do is thwart the system, make it clear that we are not consenting to their rule, as often as possible until they actually start listening; to dictate to as their role demands rather than us being dictated at.
And I think AV gives us a powerful weapon in being able to void elections which in the absence of a recall or NOTA vote we desperately need to restrain the legislature.
My yes vote is not an endorsement of the #Yes2AV camp; it is a statement that the status quo, and of having a firm None Of The Above vote summarily ignored year on year.
And anything likely to deprive Ed Balls of his seat can only be a good thing.