Worth continuing??

MattSav wrote:

Randomly, sometimes I can use the shift key for a rapid jog but other times it doesnt work, cant see any reason....

That is odd. Perhaps linked to keyboard polling and whatever is causing the other system instability problems.
There have been cases where a new keyboard has solved system stability problems, if you have any other keyboard to try, I would.
Also, you might want to look into using MPG jogwheels. They are cheap on eBay and interface on the realtime layer level so can't be affected by user-space and GUI hiccups.

and finally, usually the machines homes fine but sometimes it tries homing in wrong direction. Reboot and it will start working the correct way.

This normally means that, for whatever reason, the system thinks that the homing switch is already triggered and is going straight to the "move off of the switch" move. However, if the home and limit switches are the same thing then this ought to be triggering a limit switch problem before homing.
Is the machine driven by stepper motors or servos?

[Addendum: The advantages I claimed for jogwheels do not apply to USB-interfaced jog pendants. If you have some sort of HID latency problem on the keyboard then a USB pendant would probably have the same problem]

Aside from what others pointed out as very valid sources of problems, if you are using parallel port, you have something wired very wrong, namely grounding and interference, or something powering back to paralel port pins. That will cause all the above mentioned problems.
Quick way of testing is to remove the parallel port connector and test the computer without it. If it works normaly, check the wiring and grounding. If it doesent, change the computer.
As for reliability of Linuxcnc, I had no problems, ever.