Of course, not everything is perfect in the land of "Workstation" 2008. For starters, there's no Media Center. Media Player is installed, but there are few codecs, and of course you can't play a DVD until you scrounge up an MPEG2 decoder. Windows Sidebar, Fax and Scan, the Games folder – all are MIA under Server 2008. Ditto Vista's infamous Experience Index, which is perhaps a good move – no point in making Vista look even worse by plastering Server 2008's superior score on the System Properties dialog.
I also encountered a few minor compatibility issues. For example, the Windows Live Services installer refused to run on Server 2008. To get Windows Live Writer installed, I had to hunt down its separate MSI package. Also, the current (3.6) version of Skype crashes on Server 2008. I had to downgrade to Skype 3.2 in order to get a stable VoIP solution. OldApps.com is a real lifesaver.
One component I won't miss: Windows File Backup. Server 2008 uses a much more powerful (albeit somewhat slower) image-based system similar to Vista's Complete PC Backup option. And though you can't restore from the Previous Versions tab, as in Vista, at least you can be confident that Server 2008's backup didn't skip anything. It grabs the entire disk structure and stores it as a searchable VHD (Virtual Hard Disk) file.
Overall, my move to Windows "Workstation" 2008 has been a positive experience. I'm getting better performance, I have access to a wider range of enterprise services and applications, and I've finally kicked my Solitaire addiction, which has been a monkey on my back for 20 years now.
I'd strongly recommend that power users and other hard-core IT types take a hard look at Windows Server 2008 as a possible solution to their workstation OS needs. The easiest way is through one of the el-cheapo MSDN subscription options, assuming your organization doesn't already have a site license to Microsoft's server offerings. But no matter how you (legally) obtain your "Workstation" 2008 installation, once you experience the performance and versatility, you'll never go back to Vista or XP again.