A few non-developer have started getting Apple's invitations to try out Mac OS X Lion via Apple's AppleSeed Program.
"Apple invites you to participate in a software seeding project. Our program, Apple Software Customer Seeding, provides cumtomers with access to pre-release software so that they may explore new features, perform early compatbility testing, and submit feedback to Apple engineers. We have selected you, based on a referral and/or prior participation in our program, to assist us in testing an upcoming release of Mac OS X Lion (which now includes Lion Server)......."
The invitation asks users to agree to confidentiality just like developers and then log into the http://appleseed.apple.com with their Apple login and password. An additional password is supplied in the email.
Here's the complete invitation: