i am using it as a workstation. i used to use 2003 to host multiple websites locally and reaped the benefit of having a more stable OS compared to XP. vista now includes a robust version of IIS7 but i grew tired of its random issues both in the x86 and x64 versions. now i'm running 2008 with the full version of IIS7 and won't go back to vista on my production machine.
2008 and vista w/ SP1 are the exact same kernel core -- version 6001. the difference is that 2008 comes with barely anything enabled and it's up to the installer to turn on features like wireless networking, superfetch, desktop features, etc. because many of the heavy features like indexing and auto-defrag are disabled out of the box, 2008 feels very quick compared to vista. vista can be made to be quick but my fastest vista x64 installation was still slower than my current 2008 enterprise x86 installation.
that brings up another point... i moved back to the x86 version when going to 2008 because of application support. i've read a few tests where 2008 x86 is slightly quicker than x64 and i'd believe it. since the enterprise version supports 32GB system memory, it'll last me a long time on both my X300 and eventually a thinkstation D10 when i re-place my order after moving.
2008 is a hassle in terms of drivers. it took me a solid day to get all of my drivers installed correctly but i finally have bluetooth, WUSB, and WWAN drivers installed, all of the thinkvantage software i use including GPS and fingerprint reader, and a full desktop experience including aero and windows sidebar. unless you checked winver.exe or saw the login screen, you'd have no idea i wasn't running vista.
there are many tricks necessary to get some of the drivers installed and all i could do was experiment. one good thing about the x86 version of 2008 is that thinkvantage software update recognizes the system as "vista" and installed many of the drivers automatically. from what i've read this isn't the case with the x64 version and all drivers must be installed manually.
for anyone interested in going the 2008 route on their thinkpad, this site
is a huge resource.
with that said, vista isn't all that bad if you know how to tweak the system-loading features. as of yesterday i'm back to using vista on my X61 and am quite happy with the installation. most of the problems i had with vista in the past were due to using SP1 RTM instead of the public version of SP1. i will keep 2008 on my X300 and use the X61 as a backup in the event i need a second system to use.