All platforms: Adobe's Flash Player 10.1 is the release of the ubiquitous browser plug-in that aims to seriously improve Flash performance with hardware acceleration (on Windows computers, at least), specifically for decoding the H.264 video format that's becoming a de facto standard on the web. Today Adobe pushed out the first release candidate, putting 10.1 that much closer to a full release.
If you've been enjoying the betas, you'll probably want to upgrade to this release candidate. For more details on what's changed, check out the release notes. (PDF alert!) [Adobe Flash Player 10.1 RC1 via Liliputing]