It's not just the so-called "Post-PC" era that is kicking the backsides of Microsoft, HP, and Dell; it's the dramatic shift in the server market too. 

While Microsoft continues to dominate the enterprise server market with 71 percent of new sales worldwide (according to second-quarter figures for 2011), the Web server market is a different story.

According to Netcraft, Microsoft Web servers now account for just more than 15 percent of market share. A year ago, it was 25 percent. That's a big drop in one year; big enough to call it a trend, I think. Two-thirds of the Web server market is now sewn up by Apache.

Given Microsoft's dominance in the enterprise space, I don't think anyone has to worry about the 'softies in Redmond going without a holiday bonus this year. However, the long view is looking a bit scary.

When we talk about Web servers, we're primarily talking about servers for big public websites and their data centers; i.e. the "cloud."

Yes, the cloud! You know, that place where the future of computing is headed at a very fast clip.

As big companies like Google and Facebook, for example, build data centers to host their "clouds" of vast, vast data, they are typically doing two things:

1. Choosing open-source options (instead of a Windows server).

2. Building their own stripped down servers (instead of buying a Dell or HP server).

Facebook not only builds its own "DIY servers," but it also wants other businesses to do the same. Unlike Google, which jealously guards its homebrew server know-how, Facebook earlier this year launched something called the "Open Compute Project" educating other businesses in how to build stripped down, "no brand name" servers.

Facebook boasts that its DIY servers are cheaper, use less electricity, and run more efficiently in a cloud environment.

DIY servers now account for 20 percent of the server market.

That's a lot of lost market share for the likes of HP and Dell to swallow at a time when desktop PC and laptop sales are getting cannibalized by the mushrooming tablet and smartphone markets.

Footnote: Oddly enough, Microsoft is sort of doing the DIY server thing, too. For its MSN and Bing cloud, for example, Microsoft has built data centers running on a customized, stripped down, DIY server farm too. The difference is that its DIY servers run on Windows—and Microsoft outsourced HP and Dell to build them according to spec.