To be honest, I don't know a good font from a bad one, but one thing I do know is that one font is not enough… In your CSS that is. I am using Linux here; it's very likely that I don't have Arial or Times New Roman, or any of the other fonts the Microsoft world takes for granted. So when your CSS calls for a single Microsoft font, I'm likely to get the standard Firefox selection, which is probably a very bad serif font. The guys on Apple Macs will be little better off, and they are more likely to scoff. If you want to be as helpful as possible, you should use standard font families and provide a good list of fall-back fonts for your readers. Wiser minds than mine have put together the following lists.
Soronlin