vbarratt, this could be a tooth or gum problem, infection or a piece if sharp food stuck somewhere or poss an ear infection, basically, take cat to vet!!
Any good looking cats moved in nearby? You cooking anything nice? Of course take the cat to the vet if you worried....you wouldn't post a There's blood coming out of my ear and expect any other response then go to the hospital would you? So toot sweet to James Herriot with your pussy.
How old is the cat? Old cats, much like old people, tend to dribble. Also, cats don't really have much in the way of lips per say, that could have something to do with it... I mean, Lions are always drooling and things, but no-one has a go at them?!!