A more global set of statistics indicate that 1024x768 is indeed the most popular resolution, however the distribution of users is very different. Also note that netbooks, they suppose, are helping 800x600 hang on.
In modern browsers you can target ranges with Media Queries. They're awesome. Assuming you don't care about IE – although IE9 promises support for them. Conditional comments can be used to send a lowest-common-denominator-resolution to IE, or JavaScript can be used to dynamically load stylesheets. Loading CSS through JavaScript dynamically is, in my opinion, an awful idea.
A web designer named Jon Hicks recently redesigned his website using them, go there and change the size of your browser window to see an example of how they work. There are layouts from 1- to 4-column, depending on your current maximum viewport width.
Media Queries allow you to not have to stress about things like "Will my site support the iPhone and iPad?" or "How can I target X device's screen size to maintain usability?". You just build designs for as many screen sizes as you want to support and the Media Queries will take care of the rest, depending on the user's browser when they get there.