First of all I'd like thank the developers for this great piece of software, it was my main reason to buy an Apple TV :)
After playing around with all the options and watching some movies and TV series I was mildly positive about subtitle support. In my opinion the options for subtitles are too basic (I'm used to xbmc subtitle settings), especially the font size. Maybe it's better to give a whole range of percentage instead of 50, 75, 100%, or just point-size. Because in most situations 50% is too small and 75% is too large. It's also not consistent, some subtitles are way to large @ 75% while others are not.
Is it possible to add this as a feature request?