The leaked build doesn't need root or even a preliminary update to install; apparently you just need to check the "Unknown sources" box under Settings > Applications, and sideload the file or download it from the Xoom's browse. Engadget took it for a spin and concluded that "based on our preliminary testing, Flash performs exceedingly well on the Xoom's dual-core Tegra 2 processor."
The early build of Flash Player 10.2 for Android 3.0 still has some problems, including choppy HD playback, multitasking issues, and some difficulty detecting when to make a Flash item full-screen. That being said, low-res video content rendered at perfectly viewable speeds, and games that didn't require anything more than single-button control schemes were playable.
On the whole, it's quite good for a leaked version of a beta release. Less than a week from now we'll see how the official beta fares.