The rumors are true. Flash 10.1 is in the ROM that was ported from the HTC Desire to the Nexus One. And it works ... OK, it's not great. But remember that this is an unofficial ROM, and things are likely to change by the time we get Flash (and the new version of Sense) on U.S. phones.
A full run-down of the new version of HTC's Sense is coming. In the meantime, here's a quick video look at what's been ported over. Have at it.
Update: OK, so it looks like this is an implementation of Flash Lite, and not full-on Flash 10.1. Whatever. It's still more Flash than you've had before. :-/