I think you've hit the nail on the head. I was just thinking the same thing last week, wondering why I hate pagination when I used to like it. I realized it's the time it takes to load, which is probably due to the ads. I'm on a broadband cable connection, and some of the sites take 5-10 seconds to load the next page. One popular site a few days ago took 15 seconds to load the next page. Maybe I have a neighbor hogging cable bandwidth, but still the pages with 3rd party ads are noticeably worse.