Provider Whitepaper FINALLY available!!!
Sorry for the delay, but it will be worth it -- the 10 part, 120-page provider whitepaper is ready -- the next stage is in production now and should be ready by the end of the year.
These will be featured heavily on https://msdn.microsoft.com/asp.net/beta2/providers/default.aspx tomorrow but you can get to them now directly:
Introduction to the Provider Model
Web Parts Personalization Providers