A lot of people were upset when they found out Snow Leopard was reporting hard drive capacity "correctly" in base 10; if you were one of them, here's how you can fix it.
In a nutshell, the base-2 numbering system—a.k.a. binary numeral system—is how computers actually use space (zeroes and ones). Hard drive manufacturers use base 10 when calculating space because it makes for bigger numbers. Snow Leopard's tweak to calculating hard drive space in base 10 rather than base 2 made hard drives appear more consistent with what users read on the hard drive's box, but it's not how software actually uses space. Rather than dive head first back into this debate (read through the previous post for that), let's just agree that some people like the change, some people hate it and a lot of people don't really care one way or another.
If you're one of the people who hate it, however, a user on the MacRumors forum offers a solution with a simple executable that changes "the base number [Finder]uses to calculate sizes from 1000 to 1024". After that, Finder, Disk Utility and a few other default apps should be back to the classic base 2.