According to my sources at Microsoft, the software giant has set its sights on July 27 as the release date for Longhorn Beta 1, although that date obviously could slip if the company is unable to hit internal bug requirements. The current escrow build for Longhorn Beta 1 is 5101, a few builds older than build 5103, the current internal build in the beta 1 fork.
Microsoft recently forked the Longhorn build process to segregate the beta 1 code check-ins from the post-beta 1 (or what we can think of as the beta 2) code path. Recent leaks of Longhorn builds are from the beta 2 code path, but we can expect them to be quickly eclipsed by the beta 1 code base as Microsoft makes that milestone widely available.
As far as the beta 1 schedule is concerned, Microsoft's test teams are required to complete testing by July 22 but they need to achieve the "0 active bug" designation to ship beta 1. Yesterday, the beta 1 fork still had 123 active bugs. That number had dropped to 86 by today.