It seems that Heroes has already been renewed for a 4th season.
While ratings have been eroding, apparently the show is still doing relatively well in the target demographic. The producers have tried to come back from a very disappointing last half-season, but the show really hasn't recaptured the magic of its first season.
They are already in the planning stages for Heroes season 4 - consulting producer Bryan Fuller had this to say:
"We've spent a lot of time in the writers room talking about what season 4 is going to look like... Basically, the last act of episode 25, similar to what's been done in the past, opens up a new chapter of Heroes. It sets up arcs for a variety of characters. We set all the pieces up in terms of Claire's attitude and what her trajectory is going to be in season 4. You will have a very strong idea by the end of this season's final episode where Claire is going and what's going to be happening with the Petrellis."
I'm still watching the show but frankly I'm getting a bit bored with it (especially due to the fact that I Tivo it and watch it directly following the uber-intense 24).
What about you? Are you looking to a fourth season of Heroes or are you pretty much done with the show?