A plague on all your houses!

Anybody else think that, whatever your opinion of them, UKIP are performing a useful function by providing a "none of the above" alternative on the ballot paper? There have long been arguments that there should be such a box. which you can mark to express your opposition to all those putting their names forward.  Of course, there's the problem of what do you do if "none of the above" gets the most votes, and where, as with UKIP it does have a platform of sorts, the problem is even more acute.  But I would really like to know how many of those who vote UKIP are really just using it as an anti-the-other-parties vote, rather than specifically agreeing with the policies they are putting forward.