I use a circa-1987 IBM Model M keyboard (with a PS/2 to USB adapter) on my 2011 Mac Mini. For the most part it works well, after some tweaks in System Preferences and third party software.
However, one thing I can't figure out is whether I can send the Command signal during boot. This would be helpful for booting into recovery mode, etc. On newer PC keyboards I could just use the Windows key, but this old beast doesn't have that.
I'd rather not have to keep another keyboard around just for this purpose, although that's not the end of the world.