If you're a provider of Hosted Exchange/HMC, should should read this: http://blogs.msdn.com/gavingee/archive/2008/05/16/important-changes-to-support-for-hosting-solutions.aspx
If you've got an HMC platform then you need to have the appropriate Service Provider Support Contract in place from end-June. Microsoft are withdrawing the per-incident credit-card support for HMC, often used by smaller Hosting providers to gain support from Microsoft for inidents and issues.
We've got one and it's very very useful - not only have the global hosting support team undertaken a review of our platform so that they understand us better, we also get a named TAM (Technical Account Manager; Paul you are a hero!) with pro-active support and training from MS too.
BTW, Gavin's blog is a useful source of SaaS & Hosting news with a focus on the UK. Gavin works in the UK Hosting team for Microsoft (a useful contact for you all)