Scoble has, once again, an insightful piece:

As I’ve been going around the world I’ve been meeting with many people who’ve built their companies on non-Microsoft stuff. Some of whom have companies worth billions of dollars now. Some of whom you’ve never heard about unless you read TechCrunch. Here’s 12 reasons Web 2.0 entrepreneurs like Ross tell me that they aren’t using Microsoft’s stuff:

More...  (link on Ross added by me)

Robert pretty much nailed it.  And they're quite similar to several of the points I made when I was interviewed by Information Week back in October.  Good stuff. 

One thing that's particularly true with respect to Web 2.0 companies is that Web 2.0 stuff often starts just as "science experiments" and, since you need to deploy things out on the Internet for people to play with (and give your experiment feedback), Web 2.0 stuff tends to be built on open source tools.  That's what happened with Feedster -- I had a cheap box in a hosting center with Apache, PHP and MySQL and I built a search engine since someone posted on a blog "Wouldn't be cool to have a search engine for RSS content".  Now if I had to worry about software licensing and such, I almost certainly wouldn't have.  Now it wasn't just that open source was free -- it was also the whole ecology of cheap hosting, downloadable source code, great online docs, etc.  And its really, really hard to see how Microsoft competes with that.