The system-defined fonts caption, icon, menu, message-box, small-caption and status-bar are not supported by the shorthand CSS2 'font' property. Test case at http://web.nickshanks.com/safari/font
Reassigning to webkit-unassigned, to make sure more people see this.
Fixed. Note that I did not agree with the font sizes mentioned in the test case attached to this bug, so the font sizes chosen are a little different.
r15888 with layout tests in r15889
Those font sizes quoted were at the system's 72 dpi setting, so are in px units, not points. If you set some text to the sizes mentioned using TextEdit, you should get the same (that's how i discovered the sizes given, trial and error, using whatever version of the OS i had installed on the 15th of April 2005), but I assumed it's best to use system functions such as +[NSFont systemFontOfSize:NSSmallSystemFontSize] and its ilk to generate a px size, then divide by 0.75 to get a 96dpi point size (or other value for other dpis).
One problem I noticed: the specified fonts aren't affected by zooming the text size. Is this really a good idea? I think they ought to be the same as the system at 100%, but grow and shrink along with the rest of the text. I am going to re-open this, but if you think that's correct behaviour, just close it again.
Ah yes, that was not intentional (and is in fact a regression, since form controls aren't going to swap out to larger sizes as you zoom).
Ok, fixed in r15922.