I just updated my ASP.NET MVC 1.0 application to use ASP.NET MVC 2 RC. It was a pretty painless process. Be sure to follow the Release Notes on the download page, and many applications will be ready to go. Here are some extra things that might help get you unstuck:

• If you're using the ASP.NET MVC Futures (Microsoft.Web.Mvc) assembly, be sure to download the new one that works with ASP.NET MVC 2.
• If you're using the Telerik ASP.NET MVC components, be sure to download version BETA 2009.3.1218 or later.
• Way, way, way back in the ASP.NET MVC 1.0 beta days, they had a very nice mechanism to update lists of items by tying UI fields to index numbers, so you could use primary key identifiers to help keep track of what fields were modified where. In the 1.0 RC release, Microsoft changed how it worked to do things sequentially instead. I was using the IndexModelBinder found in that thread with great success ever since then. However, Microsoft added back in the index support to ASP.NET MVC 2 RC. This means that you will have to delete the old IndexModelBinder since it won't compile anymore. Thankfully, I didn't have to change a line of my code. Nice job of code compatibility!!