Papa I don't really take much notice of poles I know that one two have given the top spot to the Lib Dems but I wouldn't put money on what they say. I just have that feeling that the Lib Dems are going to do very well. We are getting nothing new, out of new labour and the cons have really gone off the boil. The next debate going to be very interesting.
I agree that opinion polls are just snapshots of how the people are thinking at a particular time and even if they are not all that accurate I think that they CAN influence voting just by suggesting who is leading the poll. The polls nearer the time will be the ones to watch as they are often spot on with their predictions.
I, like you, hope that even if the polls are not all that accurate they CAN make people change their vote so that they are no longer voting for the perceived losers.
The Liberal Democrats have been suffering from the "first past the post" system for many years as they often get very high shares of the vote without gaining many extra seats.