I bought a single 10×10 pixel square for deano.com way back in the day… And for years, even that tiny, microscopic, and ill-placed square was delivering me a daily hit or two.
(Yes, people still click on mine… can you find it?)
I just checked the logs… and sure enough, this past month, I've received 2 hits from milliondollarhomepage.com.
I can only imagine what the initial traffic in years 1-2 would've been for companies with larger block ads… I tried to get the company I worked for to go in on a 3×6 banner… I'm guessing it would've been the best $1800 the company ever spent on internet marketing.
Overall, I'd say everyone "got" a decent return on investment, but that by and large, there probably are only 10-20 sites left getting any significant daily hit count from it. Still, that's a spend paid for ONCE, 6 years ago, for basically perpetual traffic being driven. Pretty amazing investment, if you ask me.