According to a study at MediaPost DVR users actually watch more ads.
"Most importantly, the research concludes that DVRs "recapture" TV commercial exposures that otherwise would have been "zapped" by non-DVR viewers. The study estimated that 51 percent of non-DVR viewers zap TV commercials, usually by using their remote control to change the channel when they come on. However, 96 percent of those viewers actually watch TV commercials when they become DVR subscribers, albeit in fast-forward mode.
I suppose this depends on how people use DVRs like Media Center or Tivo. I rarely watch live TV any more, unless it's a live event I want to watch - even then I'll record it and start watching it after it starts, so I can skip through the commercials or the boring bits (for example when watching the Oscars I skipped through all the ads and the "sounds of the Oscars" showing what had just happened, by the end of the show I was watching in real-time again). I'll especially do this while watching a baseball game, I can skip through the slow parts of the game and just watch the action, I can leave the game on and go into another room to do something, if I hear some noise that sounds like something good is happening (a rarity with this year's Mariners) I'll go back and rewind to watch what happened. I've got used to how many times I need to press the skip forward button to get through a typical commercial break so I see few ads. From time to time I'll be skipping and see briefly something that looks interesting, but that doesn't happen very often. I basically don't watch ads. For a show I really like such as The West Wing I'll edit the file before watching with DVR-Edit (search http://www.thegreenbutton.com for a copy) and strip out the ads - with a show that's filmed in widescreen it's easy to manually find the transitions between show and ad, so I can strip them all out and watch the show uninterrupted.
I may watch more TV now, but I only watch what I like and I see maybe one or two ads a week.
Do you think you watch more ads when watching TV with a DVR?