The problem with substituting fonts that look similar but aren’t actually of the same family is that they can be of widely varied sizes.

For example, on that site look at the difference between Bookman Old Style and Hoefler (the second row in the first table.) You’d need to use some sort of browser detection to then set the size of a font, because one font’s 12px size can still be larger/smaller than another font of the same size…

Right now Webkit (the engine that runs Safari’s CSS rendering, among a bunch of other, smaller programs) has already implemented Web fonts, which is a CSS3 thing. Give it a search.

I hope that someday all browsers adopts Webkit, or at least everyone gets on to the same rendering engine…which would make our lives easier 10fold and websites cheaper all around.