Okay, there's something weird going on here. I realize that not everyone sees the same ads on every visit, but I just perused through the site on my 56K connection (which is actually more like 33K) and without logging in (so I see the same thing as everyone else).
I got a Windows XP Flash ad on the main page. It took up about 80% of the browser viewing area on my 800x600 resolution. Pretty bad, BUT it closed automatically after five seconds. From then on, the only ads I got were the banners embedded into each page. I checked out several pages of various types and got nothing. No more Flash, no pop-ups, no pop-unders, no ads with sound. And the interstitial ad ("Continue to Planet GameCube") uses a cookie so that it should never occur more than once in a 24 hour period.
For those of you who see a Flash ad or pop-up/under on seemingly every page of PGC, consider the possibility that it isn't our site at all. There is such a thing as "adware", which is installed on your computer by a variety of applications, most of them free and seemingly benign. (Gator is the most famous example.)
Whether you have ad problems on PGC or not, I VERY HIGHLY recommend that everyone get a program that removes adware. The best one I've used is LavaSoft's Ad-Aware, and it's totally free. You can download it from
http://www.lavasoftusa.com or
http://www.download.com. The program is easy to use and will rid your PC of adware, spyware, and all other sorts of nasty stuff that you don't want on there. Just realize that if you continue to use programs like Gator, the adware may be re-installed on your computer even after the cleaning. The best way to check is to run Ad-Aware, then run it again a couple of days later. If the scan shows some of the same stuff both times, you're using at least one program that is installing that crap on your computer without your knowledge. From there, you should be able to keep scanning and narrow it down to figure out which programs are doing it.
Sounds like a lot of trouble, but having a clean PC is so worth it. And if adware is the cause of your browsing frustration, the difference will be amazing.
(Edit: Fixed URL. Thanks Dan!)