Whatever I imagine happening over the next four years seems to end up with either the LDs being indistiguishable from the Tories - in which case what is the point of not voting Tory - or them taking the rap for most of the problems along the way. The implications of that is unclear but more likely a strengthening of Labour against the Conservatives

I actually doubt that the Lib Dems will become Tories - there's far too much anger inside the camp as it is. What I do expect is that more bad news will be shunted on to Lib Dems. I'm not expecting them to get anywhere near power until I'm 40.

AV is fairly simple, and I can explain it thusly:
1) Rank your candidates in order of preferences
2) Count up all of the highest preferences
3) Does someone have 50% of the vote
3a) No? Then remove the person at the bottom of the list and reassign their highest preferences. Then go back to 2
3a) Yes? Then that person wins the election.

There is also a cat video that explains it.