I´ve had a trial version of Windows 2000 Server running on an old box as the main office file and print share but since it was a trial and I didn´t need a full blown server installation, I decided to take a look at other options.
When the server died for no reason last week because the hardware is getting on a bit, I decided to get a spare XP box I had and use that. It only took a couple of hours to set up and replace the other server so I don´t think I´ll bother with the Server OS in the short term.
I would have gone with a Linux box since it works at least as well and is free, but this one was already lying around, plus it lets me run windows apps on an "unused" PC if I need too.