=== problem ===
ScalaDoc currently specifies "Arial".
=== analysis ===
Arial is not really engineered for technical documentation.
Additionally, not everyone has it.
To summarize, this is not good.
=== enhancement recommendation ===
After testing I came to the conclusion that something along the lines of "Ubuntu", "Droid Sans", "Trebuchet MS", "Lucida Grande", "Lucida Sans", "DejaVu Sans Condensed", sans-serif; would enable good quality font use on major platforms (Ubuntu/Linux/Android/Apple/Windows).
Ubuntu: Best differentiation between l/1/I and O/0 etc. Standard on Ubuntu, popular on Linux.
Droid Sans: Stable properties with wide range of supported glyphs. Standard on Android, popular on Linux.
Trebuchet MS: Stable font available on all Windows platforms, popular on Linux (with MS core fonts).
Lucida Grande: Available on all Apple machines.
Lucida Sans: Available on Windows, shipped with Sun Java.
DejaVu Sans Condensed: Available on Linux. Wide range of supported glyphs.
The chosen fonts have all the same glyph height and shouldn't cause any major differences (except the occasional different linebreak in texts).
The monospace font should be left undefined as currently.