I'm looking to upgrade my entire computer system at the end of this year/beginning of next. I am currently looking at different LCDs for purchase and noticed that some mention "contrast ratio." What exactly is this? I noticed that a Viewsonic 18" LCD has a 600:1 contrast ratio and a price tag of 600 dollars. Why then, does another Viewsonic 18" LCD monitor have a lower (550:1) contrast ratio, but cost more (650 dollars)? Oh, the Apple 17" has a contrast ratio of 350:1. Thanks in advance.