TiVo has not given up on its controversial idea of selling commercials that would blot out the spot a broadcast or cable network is running. "I think it's going to happen," said Stacy Jolna, chief programming officer for TiVo Entertainment Group, at a Reality Bytes Internet conference panel session in New York last week. "It's a model that's going to be interesting." But he quickly added that the company will probably have to share some ad revenue with the networks. One of the great fears of the networks-many of which have bought minor stakes in TiVo-is that the companies will beam owners of personal video recorders commercials that would overrun spots for which network customers had paid. So far, that hasn't happened: The primary challenges are scale and software. TiVo has deployed fewer than 200,000 units, not yet big enough to launch an elaborate ad scheme, particularly since 50% of TiVo users fast-forward through commercials.