Perhaps the most extreme sign of this trend is the Server Core installation option, which completely leaves out a graphical interface. The server is managed through the command line, just as you might manage a Linux box. Maintenance tasks can be automated through the new PowerShell, or the older Windows Script Host shell interpreters. The result is a server that takes fewer resources and offers fewer attack surfaces.
Even the little signs are good. Remember that Windows 98 was released in August 1998, when the year was more than half over? It looks like Microsoft will ship Windows Server 2008 in the first half its namesake year, almost like a new car model. It's nice to use a product that doesn't sound like last year's news.
The servers I use with Windows Server 2003 are hosted by a managed hosting company, so their staff will need to get up to speed before we'd make a jump. Plus, the best time to switch operating systems is when you need to switch server hardware. We don't plan on needing to refresh the hardware until late this year, or perhaps even 2009. But when the switch does happen, I feel good about installing Server 2008 on the boxes.