There has been an argument raging on about contrast rates for months if not years to be honest.
The higher the contrast rates the better the picture quality (ie contrast).
If you have a quality brand LCD 800 or 1000 would be fine. Plasma's have higher rates some 3500 etc.
However a friend has a Toshiba 28" LCD with 500 contrast, mind has 1200 and can't really see any difference. It's not worth losing sleep over to be honest.
Have a wander over to the AV Forums and have a search on there, many arguments on there, but I can't see any difference with mine.