Read the piece at Comment is Free
Why people are so angry with the Lib Dems is not because they have had to make policy compromises, but because they seem to have reneged on these key values. Political parties entering coalitions often have to compromise, but tend to be constrained in doing so by a core set of stated principles. Many voters don't think that happened this time round.
That's also why the Tories have survived relatively unscathed. Yes, they have broken many pre-election promises, but they have broken promises in a way that voters understand is nevertheless entirely consistent with their underlying values. By contrast, fairly or unfairly, voters see the Lib Dems as having gone against their values. And as Gordon Brown found out over the abolition of the 10p tax rate, it can be hard to recover from that.