Here's the first thing I would do if you are a developer of .net 1. BOOKMARK THIS PAGE! It will save you a ton of time as you migrate your apps. Then as you find a broken namespace in your app, or something else that no longer works in Beta2, click one of the links below and search the page (Ctrl-F for IE users) for your term. These documents are part of the downloads found at www.ASP.net.
Here is the change list
API Changes (thanks to Alex Lowe from ASPalliance.com/aldotnet/">http://www.ASPalliance.com/aldotnet/)
ASPx.com/b1to2changes/APIChanges.ASP">API changes broken down by Namespace