RIM has provided some good guides on how to setup BIS 2.5 and what you can do with it. Remzi has done me a favor and emailed a few my way. Let me know if I missed any.
What is required to get BIS 2.5 to work – Essentially tells you that you need OS 4.5+ and tells you how to resend your service books.
Good reading if you want to familiarize yourself with all the features. Let me know if I missed any.