It seems appropriate that a company based on a campus that feels like college would have an alumni network. One of the things they tell you about on your way out of Microsoft is MSA, the Microsoft Alumni Network. For a hundred bucks a year, or less if you do multiple years, you get access to the company store pricing (hooray!), half-off MSDN subscriptions and access to all kinds of bigger picture discounts on wireless service, health care and what not. It has some nice benefits that easily pay for the membership, and a lot geared toward entrepreneurs too.
It's almost a little surprising that the company cooperates, because it feels weird to do favors for people who left the company. I'm not suggesting that they're all big deal contributors, but presumably a lot of people leave because they can find a better deal or be challenged elsewhere. My motivation was largely geographical.
In any case, next time I have to renew my MSDN subscription, it's nice that it won't cost a ton. Continuing to get discounts on hardware and software is also a pretty nice perk, for keyboards and Xbox Live subscriptions alone. My keyboard is getting a little mushy on some keys.