<p>I learned about <a href="http://www.microsoft.com/bizspark/" rel="noreferrer">Microsoft BizSpark</a> the other day and started the sign up process.  Has anyone else heard about it or had success with it?</p>

I can't speak for BizSpark specifically (it's so new), but Microsoft has had the similar
Empower
program in place for 5 or so years. When our company was originally getting started, we joined the program (and participated for two years) and it was an excellent program.
The main benefit, of course, is that you get access to MSDN Subscriptions at such a low cost. Aside from that, though, it put us in touch with the local Microsoft office and gave us a clear path to working toward the typical ISV Partner relationship. You also get some technical support incidents, which are handy when/if you need to escalate an issue you're running into.
The requirements for Empower were/are pretty straightforward... basically commit to releasing a commercial software product based on the current Microsoft stack within two years.
Hope that helps... I look forward to hearing more about how BizSpark is different - or if it's simply the next evolution of Empower.