Paul Walter is right to highlight the Tory blunder in Henley where they are issuing a leafelt claiming the Lib Dem candidate does not live locally when if they had bothered to check their facts they would know that he does actually live locally after all !
This sort of early cock-up can cripple a campaign early on as it can be referred to again and again by the agrieved party as evidence of a dirty tricks campaign and a sign to the electorate that if they will lie about this, they will lie about anything.
Certainly in past campaigns I have been involved this sort of mistake has proved costly. In North Norfolk in 2005 Tory claims that Lib Dem Norman Lamb had "promised" to move to the constituency and had lied about this were found to be untrue, with the Tories forced to apologise in one of their elections leaflets. This mistake put the final torpedo in to what was already a sinking ship of a Tory campaign. It was certainly something that I used when wavering Tories spoke to me.
I remember too in Romsey in 2000 when the Tory campaign claimed their candidate was Hampshire "Born and bred", that the Lib Dems were contacted by someone who said they knew he was not. Further evidential proof was found to highlight that this Tory claim was untrue, and it aided the unravelling of their campaign there.
Will the Lib Dems use this effectively (and by that we mean as something to use when canvassing and when designing leaflets), it remains to be seen. But it's a schoolboy error, that's for sure.