MacUser UK has an article on the upcoming Mac OS X Beta:
Apple is planning a low-key roll out of Mac OS X beta, continuing fears about negative reaction from users pushing back the roll out of its next generation operating system to late September. The final version is now not likely to debut until March 2001.
From a
"Experienced Apple-watchers say the most likely date for the beta release is next week, at Seybold or in September at Apple Expo, Paris. A public-beta release at either of these events would leave time for Apple to receive and act on feedback before launching the full product next year."