We are about to embark on migrating our CRM 3.0 installation to CRM 4.0. We have a lot of custom entities, and have written a lot of code using the web service SDK, Stored Procs hitting the views in SQL for the entities, and even some Workflow and Callout DLLs. While I'm certainly not going to miss the .Net 1.1 development environment of the Workfows and Callouts, I am apprehensive about what's going to bite us hidden away in bowels of CRM. I have not had any experience with 4.0 at all.
My current gut feel is that this is either going to be fairly simple, or completely painful, with no middle ground.
Google searches have not turned up any good references, so I'm going to ask here:
Does anyone have any pointers, either links to resources, books to recommend, or even personal experiences that will ease the pain of transition?