At this quarter's MSDN Events one of the topics that we're covering is "Membership and Personalization in ASP.NET 2.0
In Beta 1 the default provider is MS Access - but this is changing for Beta 2.
Shanku Niyogi, ASP.NET Group Program Manager posts as follows.
Access Data Providers
In Beta 1, ASP.NET application services such as membership and roles include Access data providers, and use them by default. In Beta 2, however, we will replace this functionality with support for SQL Server 2005 Express Edition, the new version of SQL Server which combines the file-based simplicity of Access databases with seamless deployment to full editions of SQL Server. The developer model of using the application services stays 100% the same, but the backend implementation will now be much more robust and performant.
To check his blog post on many changes in Whidbey CLICK EHRE.