I've been getting several variations on this question lately:
I've heard that Microsoft is doing a private beta instead of a public one. How do I get into it?
There are two ways to get into one of our private betas . First, if you work for a large company, talk to your Microsoft account representative. We here in MacBU rely on account reps to nominate people from the companies that they support. The account rep knows the technology at your company, and they several people there very well. That makes the account rep uniquely situated to know whether a particular customer is going to be a good fit for our private beta.
If you don't work for a big company that has a Microsoft account rep, all hope is not lost. There's another group of people who often participate in our private betas: our MVPs. I should probably write more about MVPs in another post (they're awesome people who do an amazing job of helping out other users). To be nominated for a MVP Award, you have to be an active contributor to online communities, helping out others use our software. Since our MVPs are Mac users who are highly engaged with our products, and often working with them in a mixed environment, we know that we'll get high-quality feedback from them when it's beta time.
Emailing me to ask to get into a private beta is very unlikely to produce the result you want. If I nominate someone to participate in a private beta, it means that I know them, their users, and their environment very well. Emailing me out of the blue, even with an essay about how great you'd be in a beta, doesn't give me enough information and experience to know whether you'll be a good fit for our beta.
 Actually, for the sake of completeness, I'll say that there is a third way. For current full-time Microsoft employees, we make dogfood versions available internally. Dogfood starts off when we're in alpha, and usually gets updated throughout the development cycle. If you're an MS employee and want to dogfood our latest and greatest, email me and I'll get you pointed in the right direction.