The problem that's troubling us all at the moment is the prospect that, based on current opinion polls, Labour could come third in the popular vote but still be the largest party in the Commons and thus could form a government with the support of minor parties, most likely the Lib Dems.
Would proportional representation solve this problem? Well, it would mean that if Labour came third in the popular vote, it would come third in the number of MPs, but that would make little difference as to whether Labour and the Lib Dems could ally and form a government. There would be a different balance within that alliance, but it would still be an alliance of parties neither of which had come first in the popular vote - a result in which none of the electorate gets the result they voted for. PR is not a solution to the current problem.
What we need is to introduce disproportional representation - a system where whichever party gets the highest proportion of the popular vote, regardless of how small the margin, gets given enough seats to form a majority government, thus giving the maximum possible number of voters the result they wanted. The problem then is that the result is the same regardless of the size of the majority. One solution would be that the size of the majority determines how long it is to the next general election - say between two and five years.
Now I admit that this isn't a perfect solution, nor indeed a very thoroughly thought through one (you should hear some of my ideas on organizing Formula One Saturday qualifying), but at least it tries to address the problem we have, rather than being a simple knee-jerk shout of 'PR' regardless of the problem that the electoral system actually faces.