I am a lover of linuxcnc. Using either the printer port or other external interface cards - Rock solid. Any bugs that are found are fixed pretty darn fast. Pair Linuxcnc with mesa hardware (very inexpensive) and you have an industrial grade control.

Current released version change log
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Released_2.6.X

Next release version change log (you can test it now if you want) 2 exciting additions - support for mesa Ethernet connected interface boards and the new trajectory planner. (unknown at the time that it was funded by tormach and given back to the community) - Tormach used linuxcnc for their new control.
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Released_2.7.X

I have used mesa hardware in my systems and have found it to 'just work'. The owner is also very active in the linuxcnc community.

Linux isn't as scary as others would like you to believe. You do not have to be a 'programmer' to use linuxcnc. Between linucnc's HAL layer and its integrated ladder logic - pretty much anything is possible without writing a line of code. (although you can if you want to.. There is a C like language that allows you to write realtime components for your system - not to mention you have access to the source code) most people only scratch the surface.

sam