[ellson] Assuming you have graphviz built with pangocairo, the syntax for dot's fontname attribute is pango's:
"[FAMILY-LIST] [STYLE-OPTIONS] [SIZE]"
should give you what you want.
The current version of dot ignores any [SIZE] value and uses its own default, or the value given by "fontsize=..." instead. We will investigate to see if we can at least accept pango's [SIZE] to override dot's default.
If you don't have pangocairo installed, then fontname is interpreted by the gd library and fontconfig, which unfortunately uses a different syntax:
should work. My personal feeling is, don't use graphviz without pangocairo, but perhaps we can do something to make the syntax for uniform in this scenario.
If neither pangocairo nor fontconfig are available, then we fallback to some internal bitmap fonts. In this scenario its probably best to just stick with the default font.