I had a conversation yesterday with a colleague that went something like this:
Colleague: Bet you're really glad you're not the candidate, it looks like things are getting really vicious
Me: I take it you got a Lib Dem leaflet through the door
I've got to say that from what I've seen of the leaflets, by far the most vicious and nasty campaigning has been that of the Lib Dems. In particular, they seem to be targeting the Greens with a hell of a lot focused on Rupert Read. I'm not surprised by that at all, when the Greens came riding into Norwich the first wards they conquered were the Lib Dem ones (I was living in Nelson ward when it first fell to the Greens).
Whatever I might think of the Tories and the Greens (and even for that matter UKIP, Craig Murray and the various others) I think it's safe to say that all have run clean (as much as is possible) campaigns. The Lib Dems on the other hand have been vicious, dirty and underhanded. Personally, I think they'll pay a high price for it.