I don't know, but I'm thinking what The Times' Sports Editor (no, really) Martin Samuel is thinking:

Only in our system does this damnable trade-off masquerade as democracy; only in Britain does the idea proliferate that an anti-war, pro-civil liberties voter should, in some places, give his support to a pro-war, anti-civil liberties government, just to stop an even more right-wing party getting in. Under a PR system and it really is this simple, folks — a vote for the (anti-war, pro-civil liberties) Liberal Democrats would count.

(Via MakeMyVoteCount, an Electoral Reform Society co-production)

Actually, I like it the way the Greens' materials put it: The only wasted vote is one you don't believe in.

Oh, finally, if anyone cares, I've sent my postal vote off, so am now immune from all campaigning except in the sense of making me annoyed.