From what I can tell from over hear accross the pond is that the economic crisis might be the lever that get's them tossed out.
Partly true. I think the main issue, apart from the fact that they've now been there long enough for everything to be thier fault, is that whilst, technically, we elect a party, not a prime minister - the last general election, Tony Blair was PM. He stepped down, and we've had an effectively un-elected PM since.
Many people therefore feel that Gordon Brown wasn't elected... he's also a terrible public speaker, has no charisma or charm, and used to be the chancellor - so people blame him personally for the economic crisis.
Yeh. He's gone as soon he runs out of time. I'm not sure exactly how much longer he can defer a general election, but I know he's done it at least once.