Microsoft are holding their Worldwide Partner Conference next week and are tipped to show off their pre-beta version of Windows 8. WPC 2011 starts on July 11 and WinRumors noticing a tweet from an account called @MSFTtm which said "Microsoft wil release a CTP [Community Technology Preview] build of Windows 8" at the conference. Of course, a single tweet from an unverified source does not guarantee it will happen, but this particular source has been pretty spot on about previous Windows 8 builds.
On top of that, tech site Windows 8 Beta says that "two independent sources" confirmed its earlier report that Microsoft would unveil the pre-beta build at WPC 2011. They also claim that Microsoft are looking at releasing said pre-beta build to gold partners just after the conference. If the rumors are true, it shows Microsoft are quite aggressive with their timetable for Windows8.