Royal Pingdom did an analysis of what "popular" sites are running beneath the hood (as easy as a query at Netcraft). Royal Pingdom reveal themselves as a certain "persona" (yeah, I'll overgeneralize for now) by their choice of sites: Technorati, Meebo, Feedburner and so on.
It probably isn't surprising that most of these sites run on Linux with Apache and MySQL involved somewhere on the back end. I'm surprised (of course I'm not in the LAMP game though) to see a bit of a surge in the use of Lighttpd - a more lightweight serving engine than Apache.
As a developer confined to the realm of Microsoft tools it's a bit disappointing albeit unsurprising. What lies beneath the statistics at Royal Pingdom is something bigger and more crushing: the people that seem to be at the forefront of thinking and building the web don't use our tools. Our tools are the favorite of the commoditized environment of your average big company - less thinking and less innovation.
In part I can see a chicken and egg scenario: people building startups and experimenting need a cheap platform upon which to do so. One doesn't license Windows Server, Visual Studio, SQL Server, and so on with a poor [wo]man's budget when comparable free tools exist. In other words, I would assume that some market economics are behind the choice of platform.
But if you're a person like me in the Microsoft space, perhaps a big part of the frustration of working within an environment that lacks passion and quirky inventiveness is that the birds of a feather live in a different place and use a different technology. Of course I work with a lot of people who are excited and innovative - and beyond my coworkers there are quite a few people pushing the envelope with Microsoft tools. But I'd say in general that a corporate developer has a different set of values and goals than the kind of person who would build at a startup. As time passes I see this less on a "success" angle - most types seem to do well enough for themselves - and more of a clustering of similar people.
The bright spark on Royal Pingdom's list is Alexaholic built buy Ron Hornbaker which follows a pattern I'd like to follow as an ideal - that a person can use Microsoft technology (with which I'm quite familiar) and implement any good idea. Beyond that, there is an advantage to a smaller pool of innovators - there is more room for folks like me who may not have the best ideas in the world, but who are good enough to perhaps take something from the startup/open source space and port it.