If you’re having stupid amounts of trouble with your plugins loading in Safari 4 on Snow Leopard, go to your Finder and open /Applications. Right-click on the Safari app and choose “Get Info.” On that screen, you’ll see a checkbox to run the app in 32-bit mode.
Restart Safari if it’s open.
Now you’ll find that your plugins magically work. I guess this whole 64-bit thing has caught developers with their pants down. Not sure how that happened since they’ve only been talking 64-bit on the Mac and Windows side for years.