.NET
As I'm sure you are all aware that the guys have released Preview 5 of ASP.NET MVC Framework.
This preview has had a lot of changes since preview 4 and this means a lot of changes to get a preview 4 application building (and running correctly) against preview 5.
I have managed to get my application running (eventually!). Here are the main areas that I had to change to get it working:
New dlls
Almost goes with out saying but you need to reference the new set of dlls
System.Web.Mvc
System.Web.Abstractions
System.Web.Routing
...