How could one forget 1977 gromit ? As I remember, the Libs had 13/14 seats and propped up the Labour Government of the time. According to Wiki, the Libs have been in coalition with Labour 4 times, the last being in 1977.
But that was the Liberal Party, not the Lib Dems that we have now. Sometimes we forget that the modern Lib Dems are formed by a coming together of the Liberal Party and the SDP, who were nearly all disaffected members of the Labour Party. So, we are not really comparing like with like.
The Lib Dems will, as you say, get into bed with the Party with the most votes, if that party doesn't win outright in May 2015. But it is looking increasingly that Labour will be able to form a majority Government next year. There is still some doubt but I personally think that it will happen.
The Lib Dems will then find themselves in the political wilderness again, where they have been since the 1920's. Pity, as they have some good people, like the present Business Secretary, but in the end its always a straight fight between the Tories and Labour...no other party really matters very much.