The most recent case in point is True Blood, which was officially renewed for a fourth season less than a day after the third episode of season three aired. And that's hardly a record for the network, either; they renewed Treme (the best show on television that no one is watching, in my humble and never-wrong opinion) for a second season the day after the pilot aired. This fourth season will enter production at the beginning of 2011 with its twelve episodes set to begin airing that summer.
Personally I'm indifferent to this news. I loved the sexy, over-the-top, vampire soap opera antics of season one mainly because it also had the whole "Hey world, vampires are real" thing going for it, but the last half of season two was such a dire misfire for me that I lost interest in almost every single character on the show. So far season three hasn't really done much to make me look forward to new episodes once again. But maybe that's just me considering some 5.1 million people tuned in for the season three premiere, which was over a quarter more than those who showed up for season two's.