You can list as many fonts as you like, but make sure you list them in your order of preference. This will help ensure a more consistent look across Macs and PCs. Style sheets let you specify not just the font, but also attributes such as point size, indents, and letter and line spacing. As the cynical in the crowd might suspect, specifying these attributes doesn't always give you great control over the appearance of your Web pages. Because of the differences between the Mac and PC operating systems, text specified at the same point size will be rendered at different screen sizes on the two platforms.
Macs are consistent.
In contrast, Windows renders type at a notional screen resolution of 96 ppi. Mac designers hate this phenomenon because it forces all of their type to flow differently than intended. Text blocks grow in size, and there may even be misalignment between pictures and text. Whether you view it as a step in the right direction or an unfortunate straying from the rightful path, Microsoft muddied the Mac waters somewhat with its introduction of Internet Explorer 5 for the Macintosh. As a default, this latest Mac version of the browser also uses a resolution of 96 ppi for rendering fonts, to match the font handling under Windows.