Xen 3.0 is expected to be released this month (and as far as I can see from my top queries statistics people are hammering for downloading).
If you are interested in being documented as fast as possibile you can take a look at the actual Xen 3.0 User’s Manual.
This is an ongoing work so you always should check the Chapters Status to know what’s missing.
Remember you can also test the technical preview simply installing SuSE Linux 10.0.