For those of us who keep a wary eye on the Heroes ratings, you might find this live feed interesting to keep an eye on as the season goes on. As far as I can tell, it's generally pretty well informed and has a good track record in terms of past results of what gets canned or not. Anyway, as of the time of writing, comfortingly, Heroes is apparently doing well enough that it isn't endangered (yet anyway). So yay for that - let us hope for green and then we can all relax. Be warned - there's the odd spoiler for other shows in the headlines for the site visible on the page.
(If in the statistically unlikely event that you couldn't care less if Heroes lives or dies, it also has (I think) all the major network shows so you can follow your own pet show instead)