While I am not a fan of backward compatability, I am a strong fan of accesability. It concerns me that many disabled people (at many levels) can't browse the net as freely as the rest of us. What about all of those tech guys and professors who only use Lynx (on thier 15" monitors)? Wouldn't you like them to view your site? How aobut the old ladies who can't see small print...some of them have a lot of money, ya know?! Getting an older person who is a penny pincher to buy a new monitor when his 15" works just fine, is like trying to swim in sand.
Only compliance puritans and other nerds think that a website is 'perfect' once every user at every resolution can view your webpage. Christ, hey here's an idea why not spend the hours you spend on compliance with Opera(which no one uses) and use those hours submitting to search engines, buying advertising, or trading links. The fickle geeks who fret over NS3 really aren't worth adressing.