Rolling up information in SharePoint Sites
As the usage of SharePoint increases, there is a profileration of SharePoint sites. This makes it harder and harder to keep track of where your documents are located and also to see a unified view of your "stuff".
In Office SharePoint Server 2007, we are introducing a couple of new web parts that address this problem.
1. On My Site (personal roll-up)
The first one is the SharePoint Sites (the name may change by RTM) web part. This web part is meant to be used in your personal site, and it automatically rolls up all the documents created, modified, checked-out to you as well as tasks assigned to you in every site that you are a Member of.

Each site shows up as a "tab" and will show you the documents and tasks assigned to you. In addition, you can manually add additional tabs that point to any SharePoint site.

How does it know what sites to show automatically?
In Office SharePoint Server, there is a user and membership sync engine that figures out which sites you are a Member of. The engine requires that the user explicitly be in the Members group of that site. The SharePoint Create Site and User Management UI allows you to provision and manage this group by default.
2. On any SharePoint Site (Generic Rollup)
A second web part called Sites Rollup (name may change for RTM) can be used on any SharePoint site (Team site, Document workspace, etc.). This web part allows you to create tabs to each site you want to show and also allows you to specify a rollup page in those sites. It does not automatically populate the list of sites based on who is viewing the part.
Venky Veeraraghavan - PM