I just found this very intersting test report: "Legibility and readability on the World Wide Web". A couple of Argentian researchers did a test with 123 American people. Among others they tested what fonts they could read the fastest and most accurate; what the optimum number of characters per line is; and what's the best colour setting (different fore- and background colours). As for type faces, Verdana seems to be the best choice for both speed and comprehension (Georgia -- which I use -- and Comic Sans score second). Trebuchet MS is considered the most elegant font, Verdana is a close runner up. In the test for leading space and font size, 12/12 seemed to allow the fastest reading. For comprehension 12/18 is more appropriate. As for column width, 80 characters per line is the optimum for quick reading and for text comprehension aswell. The result of the colour setting test (with different fore- and background colours) is kind of weird. Apparantly you can read the fastest with a white on green colour combination (black on white is second). For text comprehension black on white is the best, though.
The font I use here, Georgia, appears not to be a bad choice (luckily, because I find it a good-looking font face). I also have around 70-80 characters per line, so it should be easy to read. The font size (14 pt) is not optimal, yet considered to be more confortable to read (according to the research) than 12 pt. And about the colour setting, there's no way that I'd change it to white on green. Eww. That would look so awful.
Anyway, I think this is a must-read for every serious web designer and everyone else who actually cares about their readers.
"Read the full report":http://bigital.com/Web_Legibility_Readability.pdf.