It's all about cost
I probably do not need to even mention the current state of the economy. But in case you haven't had your head out of the sand in the last year, the world's economy is not doing so well. This long-term down-turn of the economy has certainly trickled down into IT departments and homes around the world. Much of that trickle-down precludes the purchasing of new computers and certainly new upgrades to operating systems and software.
If you're thinking about deploying Microsoft Exchange, you can forget about it with the new licensing costs. (You have to pay a licensing fee for every user that logs into the Exchange server now!). To this end, Linux and open source software will become the savior of the PC in 2009 and forward. Why? Costs. Linux is free. You want the latest, greatest? Expect to pay nothing. You read it right - zilch, zero, zip, NADA! The Linux operating system is released under the GPL which means it is free of cost and open source. You can download it, alter it, redistribute, whatever.
And this cost doesn't end with Linux. There are tons of software applications available for free. The cream of the crop?
OpenOffice: Office suite to rival MS Office
The GIMP: Graphics tools akin to Photoshop
Scribus: Desktop publishing on par with Quark and Pagemaker
And many others. Each of these tools will save you from having to pay for costly software licenses.