I've had a couple of emails asking how these ratings are calculated, as if people are assuming they're not a straight average. Well, admittedly anything that looks like an attempt to spam the figures is excluded (there's plenty of assholes out there, you can bet). Apart from that: logically enough, I do weight reasoned opinions with comments more heavily than a simple number - and an email address to correspond with is more valued than an anonymous response.
But these ratings are not fixed in any way. They're based on the last six months responses.