I have had the beta version installed since 24 hours after M$ leaked the beta to the torrent sites. Before you challenge the M$ leaking the beta: http://www.insidetech.com/news/articles/3662-report-accuses-microsoft-of-leaking-windows-7-beta. I have traced the leak back through Googels cashed pages and I'm convinced.
As far as the beta itself. It is a very polished beta which actually feels closer to an RTM. The 32 bit version uses between 323 and 383 megs of ram at idle with Avast home AV and VMWare tools installed. The 64 bit version requires about 427 megs at idle in the same conditions. The speed is at least as fast, if not faster than XP. Both version require about 7.5 gigs of HD space. Both versions report in the logs a possible memory leak when using IPV6. This could be an artifact of VMWare. Both versions are sufficiently close to Vista that the learning curve is minimal. Both versions exhibit aggressive memory management and garbage collection; I left both versions idling for three days, as I did Vista, and the memory use went down rather than up as it did in Vista. Both versions also exhibited acceptable performance when I idled the CPU down to about 500 Mhz. I have yet to decide how to bench mark the OS or to test the security.
If someone wants to be cruel, try the old hack that crashes every version of Windows since 95. Write a program the issues three tabs and five backspaces. I have not done this... yet.
And yes, I am now using the official M$ release. Had within two hours of the reopening of the DL link.
No, I am not an M$ fanboy; I use Linux.