The problem for the Lib Dems is that they haven't yet managed to hit on an attention-grabbing issue to make their own – their favourite, perhaps only, election strategy. The cause of Parliamentary reform could have done the trick, but – beyond Nick Clegg's call to prevent MPs from taking their summer holiday – very few of the Lib Dem proposals have received much coverage. Likewise, electoral reform, which Labour now seem to be comandeering for their own manifesto.
This will always make some Lib Dems worry that other parties could sally onto their ground. In which case, I rather suspect that they're going to start making more of their opposition to the conflict in Afghanistan. Clegg has already road-tested a "Let's do the the job properly, or let's get out" message. The first half of that may well disappear before the next election.