By Mike Sergeant
Political correspondent, BBC News
Lib Dems are fighting key battles in the south west and in the north
In previous years some Liberal Democrats almost seemed to revel in opposition.
Spared the burden of office - or even the chance of power - they were free to dream and promote expensive policies.
At this conference, there's slightly a different atmosphere. Closing opinion polls between Labour and the Tories have led to palpable Lib Dem excitement about the possibility of coalition government.
Of course, it may not happen. Hung parliaments are extremely unusual in our parliamentary system.
But if it did, the Lib Dems might well hold the balance of power. The party leadership is reluctant to discuss this possibility too directly. Fearful of party splits, Nick Clegg and others have instead skirted around the issue.
From now on, everything the Lib Dem leader says will be analysed for any hint that he is tilting towards Labour or the Tories. Today he praised Margaret Thatcher's attack on the unions, and strongly criticised Tory plans to cut spending this year. Make of that what you will.
Senior Lib Dems know the challenge is to keep all the options open for as long as possible. Mr Clegg wants his troops to fight hard against their political opponents on two fronts.
That means defensively against the Tories in the south-west England and an offensive operation against Labour in the north of England.
And the merest suggestion of a cosy pre-election arrangement with either party would be disastrous for Lib Dem activists in extremely close local campaigns.
It means that "what if" questions about the Lib Dems' likely course of action after an inconclusive election are batted away.
Senior figures in the party refer to four loosely defined conditions for co-operation with any other party. They echo the party's main manifesto themes: fair taxes, a fairer economy, more money for disadvantaged pupils and political reform.
At the same time, the Lib Dems in Birmingham have been trying to send out a message to voters and the financial markets. They want to reassure anyone worried about messy, unstable coalition government. The Liberal Democrats are keen to present themselves as serious and competent contenders for power.
They claim their plans for bringing down the deficit are the most comprehensive - something fiercely disputed by the two big parties.
Labour says the Lib Dems are still trying to be "all things to all people", and still have a massive "credibility gap". The Tories accuse them of being "all over the place on the economy".
While Vince Cable would like to be seen as the reassuring master of detail, Mr Clegg will concentrate on the big picture and try to deliver the sharpest political attacks. It's a double act we'll see a lot more of in the election campaign.