For what it's worth, in this completely unscientific survey, much less than 1% of all visitors to my site use 800x600. There are 15 more popular resolutions ahead of it. In fact, twice as many people show up on a mobile device with 396x320 resolution (aka iPhone).
For whom? You? Or your client/employer?
There are millions of people, credit card in hand, who will just click somewhere else if they have too much trouble with your page.
My clients don't want to leave a single penny on the table. They're the ones who determine the tradeoff, not me.