About a month ago I discussed how Microsoft intends to take an open source approach with the .Net Framework 3.5 code - to allow for easier debugging.
Now it looks like Microsoft will actually share the source for Visual Studio 2008 with select partners.
The program is limited to "premier partners in the Visual Studio Industry Partner Program" a tier that currently covers around 85 partners and costs $10k/year with a 3 year minimum (what I would call "give us $30k" program).
The good news here are, that for the first time, partners are allowed to develop VS applications and plugins or on other environments than Microsoft's Windows (maybe an integration with Linux tools? VS on Mac?)
I sure hope my company has access to that source (have to find out what level of partnership we have) - this could prove very interesting.