Proportional representation is a BAD idea.
Think about it- if my piddly little party gets 2% of the vote, we get 2% of the seats. Your party gets 4% of the vote you get 4% of the seats. Every other tin pot group gets a couple of seats and what do you get? A series of unstable coalition governments that cant function and fall apart at the first hint of a policy. Like Italy or Weimar Germany.
Also, what representitive do you lobby? You don't really have one, because all of the seats in parliament are distributed according to percentage, not to geographical area or constituancy.
We have proportional representation in our Senate. This works rather well because, 1stly, government is formed in the house of representitives, not the Senate, so you don't get unstable coalitions, and secondly, the government (usually) has to negotiate with the minor parties and the opposition to get their legislation through, so it acts on a check on executive power. I would not want proportional representation in our house of reps!