I've always preferred the Electoral Calculus calculator to the BBC's but in this case they come up with almost the same result. Imagine Cameron's support firming up and Labour's collapsing further; the following vote share is not unimaginable;
Conservatives - 36%
LibDems - 30%
Others - 11%
This would leave Cameron 6 seats short of an absolute majority (EC) or 9 seats short if you prefer the BBC. Either way, close enough to form a government without a pact with the LibDems, but one constantly on a knife-edge. It's a result that would strengthen Parliament and rebalance the current tyranny of the executive. It would return power to back-bench MPs and their constituents. But as I say, a dream result ...