Real-Time Linux Experiences?

fidget42 asks: "I was wondering what types of experiences people have had with using some of the 'real-time' variants of Linux. I have looked at some of the choices (RTLinux, RTIA, etc.) but would also like to tap the experiences of the Slashdot readers. I am not looking for an embedded solution (while I will be on a single board computer, it will not be for a 'set-top box'), but one that will live happily on a PowerPC running in a VME chassis or something similar. Have you had good luck controlling VME devices from within a real-time Linux system? What problems did you encounter? While I do not need to run hard real-time, I still need tight tolerances on my timing. Our current platform gives us 5ms of jitter per 50ms cycle (very bad) and we would like to get down to 0.5ms, or less, of jitter per 50ms cycle. I also need guaranteed deadlines. One vendor told me that '97% of the time, you should be able to make the deadline' but 97%, and should, is still not good enough. Any and all help would be appreciated."