Rapidshare and Megaupload sucks! I don't know why there are many people are still using it.
Many movies, ROMs are hosted on Rapidshare and Megaupload with a random name("3tgf93.rar") and .rar as file extension.
They both need to wait for 30 to 100 seconds, and Megaupload has popup ads of partypoker, a gambling site.
Rant about Rapidshare and Megaupload here.

I don't get many popup ads like you do. I do agree that the time limits they add are annoying.

Most popups are blocked.
I found some Greasemonkey scripts to remove the wait time.

I try to avoid those download sites, as they tend to throttle your download speed.

Edit: Oh, you can't forget the message that says "Please wait 405 minutes before starting your next download."

Rapidshare and Megaupload's time limit is JavaScript, so you can find the variable that holds the time counter.
I added a poll, scroll up)

I prefer Megaupload because the download limit is less than rapid*****.
Mediafire is awesome because you can search it on google and there's no limit!
(Everything I download is legal)

Mediafire.

No time limit = instant win.

YES, MediaFire rocks.
I only found illegal stuff on Megaupload and Rapidshare.