The footer on this blog already mentions the use of a technique called Progressive Enhancement. But even more important for a website is proper typography. And with typography I don’t mean usage of snobbish fonts (although I must say the Gill Sans looks great), it means using proper font-sizes, line-height, colors etc. Text is there for reading, not for filling up the page. This means that the text has to be optimally readable.
Imposing that the computer screen you’re currently reading from is about 50cm from your eyes, the font-size should have the same size as a book or magazine at just 30cm. This means that font-size of paragraphs should be at least 17pt big.
More on this subject on the Information Architects blog