Right on the heels of the Internet Explorer 9 beta, Adobe is talking about their upcoming 64-bit Flash plug-in called "Square". This new version of the plug-in should run fine in a 64-bit browser like the new IE9. The preview of this new plug-in can be downloaded now for Windows, Mac, and Linux. Open source nerds are pleased with that last point. They have traditionally been left on older versions of Flash.
Adobe is claiming that users will see a performance increase, although they were light on the benchmarks. They did say that the there will be a 35% increase over older versions of IE in Flash performance, but it's hard to know how much of that is thanks to the new IE9 engine. Have you tried the preview? Noticing any speed improvements?