Most TiVo users love skipping past the commercials but that's about to change for some. The 1.2 million users that download their programs directly from the company will start seeing pop-up ads filling about 25-percent of the screen when they try to fast-forward through commercials. The 2.1 million who receive their TiVo service through DirecTV won't be affected unless DirecTV decides to get in on the game.

General Motors and The WB Network are the first advertisers to sign up for the pop-up ad service. When the pop-up ad appears, users can push a button to see longer promotional information from the advertiser.

A spokesperson for TiVo says there will be no way for users to opt out of the pop-up ads.