We've been using the Database Access Application Block (DAAB) in Enterprise Library 2.0 for our .NET migration effort and have found it to be a great way to jump-start our development effort.  We are using the Enterprise Library as-is and are simply implementing our own versions of the Database and DatabaseFactory classes.  As we eventually get the "production" version of Enterprise Library 2.0, we'll simply deploy the new assemblies along with our own assembly that implements our custom classes ...