I had the exact same problem on my 10.4.11 version (mac book). All of a sudden, I couldn't go to espn.com or youtube. On espn.com, every one of my browsers (safari, firefox and camino) would hang within a second of hitting the page. On youtube, as soon as I finished watching a video it would happen. I could speculate but what's the point?
Anyway, I solved my problem by downgrading my flash player. First, you have to uninstall the flash player that you have. Close all browsers and download
this uninstaller. Run it, then restart your machine. Not sure if that's necessary, but I did it. Next, get the previous version of flash
here. It's the 74.7MB download. The 9r115 version of flash is the one that's crashing for everyone. I installed the 9r47 version and haven't had a problem since doing that. When you unzip the download, you'll see a number of other 9+ versions as well.
It seems that Macromedia isn't all that gung ho about finding a solution to this problem, so your best bet is to downgrade for now. I haven't read the specs to see what's the difference between the two releases. However, I haven't noticed any issues with the 47 version. Good luck.