Be careful, Kuwait340: As far as I can remember, the GS is reset to 0 after 2 minutes after onblock, but the bias remains, and will only be reset to 0 if you realign...
So it may seem that GS is usually 0, because by the time you look, it has already reset itself - while you were busy reading parking checklist, noting onblocks, remainingfuel and thelike....
Nic