Adobe has released an update to Flash Player 9, which fixes an issue with flash uploads in Leopard. If you use Flickr's multi-upload feature or other sites that take advantage of the FileReference.upload() function, it is definitely worth installing this update. Make sure to run the uninstaller (linked in the release notes) before installing the new version.
In addition to fixing the Leopard upload issue, the new release candidate prerelease (say that three times fast!) features, among other things, H.264 video support, HE-ACC audio support, scalable full-screen mode and multi-core support for vector rendering.