What really got me was back when the Battlestar Galactica pilot screened on TV. I was very keen to see it, and heard the pilot was three hours three minutes long.
It was split up, on TV3 I think, into two 180 minute slots, which means there were almost as many minutes of ads as there were of the show. I had to turn it off after one scene was interrupted in the middle for an ad-break that was longer than the scene, then we came back for a single line (now out-of-context) and one camera change, then cut to another break. (For reference, it was a scene with the nuke hitting the Galactica, then six minutes of ads interrupted by about 25 seconds of show.)
I turned off my TV, found an email address, and explained to them just why I was going to buy the DVD and not watch another second of their broadcast.
TV advertising is so intrusive these days that I haven't watched broadcast TV in years.