I think NASCAR is boring as sin. It's a bunch of cars that are under so many restrictions as to make them virtually identical, which would be fine as a way to test the skill of the individual drivers, except they're on the absolutle simplest track you could have short of a straight line. F1, Le Mans and GT type racing is way more entertaining, as they have to turn in two entirely different directions at a variety of different angles. I flipped on the TV last weekend and they were running Le Mans racers and GT racers on Road Atlanta at the same time, which I'd never seen before (which goes to show how often I watch racing); I was transfixed. That was a million times better than watching some rednecks turn left for three hours then hold a press conference where they explain the intricacies of how they didn't turn left up to their usual standards of turning left and how next week they'll surely turn left better because next week's track favors their particular style of turning left.
That said, I find racing to be far more enjoyable in the form of video games. I have a hard time watching any form of televised racing for very long, because it is all very, very similar; if you've seen one lap of the race, you can extrapolate it to the remaining 299 and save yourself some time. In a video game, at least you have a feeling of attachment since you're actually in control, even if you're doing a straight simulation of the race that you wouldn't watch on TV because it was too boring.