Also, is there a way to specify alternate stuff for the various output media types? I know I've seen that feature in other software...
One question at a time! ;-)
Do you mean, say: A different graphic for output to HTML? I don't think we have that, though I could be wrong. But feel free to file an enhancement request. I don't think that would be very difficult.
Oh, no wait, we do kind of have that. You could use branches. Have a "PDF" branch for your PDF stuff and an "HTML" branch for the HTML stuff. Not perfect, but workable.