This has been shot down so many millions of times...
The issue is that you click "agree" when you agree with the content rather than when you think it's a well-written post. In a thread about GT5 impressions in a few weeks, one person could say "GT5 IS AWESOME I LOVE IT" and another could say "I personally find Gran Turismo 5 overrated, for these reasons: x, y, z... but it's still a very good game", and while Post 1 has little worthwhile content, because it panders to common opinion, it will have a much higher rating.
The system would do nothing except divide the user base. It's not a reward for a quality post. Just look at (ugh) N4G.







