According to an article on the Hollywood Reporter the season 3 premier of Heroes brought in 25% less viewers than last seasons premier. The 2 hour episode ranked second behind Dancing with the Stars in the 9pm slot and behind CSI: Miami in the 10pm hour.
I have yet to watch the premier, the 9 month hiatus kind of lessened my interest in the show. I guess out of site, out of mind is pretty accurate. I will probably catch it online. I miss the old season schedule where you knew when your favorite shows were going to air and seasons started and ended in a predictable manner.