The rating system was originally intended to serve as a reflection on the character of an individual. My belief when creating it was that the personality you exhibit on these forums is your personality, period. There is no real freedom to screw around in one forum such as the lounge and not expect it to have a negative impact on your rating.
So the impact of your behavior carries through the entire site. This approach requires far less work than rating individual threads, for example.
This system was also designed to be something of a social experiment. We had no idea what impact this would have on the community. I must admit that on the whole it *seems* as though crap posting has decreased.. but it's probably too early to tell. At the very least with the moderation flags it may mean that problematic posts are being dealt with much, much more quickly than before.
So why tweak it? Well we knew from the outset that it would probably have to be tweaked. From what we can tell so far it seems to work in a pretty stable manner. Our biggest concerns were with seeing wild fluctuations or massive rating spamming.
What I see now though is what I originally hoped I would see. There is more and more of a smooth continuum of ratings from probably the 800 level up until the 2000 level with each day. Fruny has even managed to surpass the moderator base with his own rating.