I've actually qualified in two of those at Pokerstars
where I got about 20th place (once I made top 27 I just didn't care), although the fields weren't quite as huge. They were something like 6k and 8k. That was after a lot of attempts though... it's not exactly the most fun or rewarding poker you'll ever play, and even making it into the top 100 is quite the achievement.
And then, it's funny, I actually got FIRST (not that I won anything special for it) in one of those, on a Limit Stud Freeroll. I never ever play Stud, it was the first I'd played it on PS, and I generally didn't feel like I knew what I was doing, so it was really odd.