VSIP SDK is essential for integrating tools seemlessly with Visual Studio. Last time I asked about the VSIP program, quoted price was ridiculously high, near five figures I think. Now it is free after registering and agreeing to terms as a VSIP Affiliate. Severest clause in the agreement seems to be that you are required to upgrade your tools to be compatiable with new versions of Visual Studio within 180 days of release.
I don't know how much Chris Sells has to do with it being free, but I suspect he had a lot to do with the change. Thanks, Chris. Maybe if enough bloggers get a job at Microsoft fulltime, we can drop prices across the board. Just kidding.