This looks to be very useful indeed. Found it on the Devhawk blog. Here's some blurb from the page:

Summary: If you are involved in designing and developing applications, you probably need to control how users interact with your applications on a case-by-case basis. For example, administrators, managers, and employees may need varying levels of access to your applications, and in some cases an individual user may have different roles in different applications. It is a significant challenge to enable this flexibility, particularly in situations where administrators maintain account information in different authorities and user databases.

The Authorization and Profile Application Block is a set of reusable code components that you can use to customize the behavior of an application for individual users. This guide describes the design and features of the Authorization and Profile Application Block and demonstrates how you can use the block in your applications.

Similar functionality is supplied in Whidbey (ASP.NET 2.0), but this does looks just stunningly useful. Support for Profiles in a 'standard' manner (which looks very similar to the Whidbey implementation at first glance) is just incredibly useful - how many times have you supplied this functionality, in how many different ways?
I really recommend getting to know and love the Application Blocks, I use the Data Access Block and the Exception Management Block pretty much all the time now, they help enforce best practices and save a whole load of typing!