beware of font's you don't have installed
Everybody is talking about CSS fontstacks and there are plenty of good lists/combinations out there but do not use them carelessly - like the prototype.js guys did (@see screenshot). DO NOT use «Helvetica Neue» for your bodycopy or fontsizes smaller than 18px!
CSS 2.1 - some interesting things about specifications
According to the Specification (4.1.3 Characters and case), identifiers can contain only alphanumerical characters [a-z0-9] and - big surprise - ISO 10646 characters U+00A1 and higher, plus the hyphen (-) and underscore (_). That's totally new to me and I've never ever