I think the descriptions on the webpage are informative, so I would put something similar on the button subtitles. For example: "fill in missing data" and "overwrite any entry".

My main need for Hermes is to get photos for my existing contacts, as most of them don't have a photo in Gmail etc. I would prefer to check their birthdays in Facebook rather than from my calendar, but that's just me! And I will remove the birthday-only contacts, I'm oldfashioned enough to think that contacts need to have phone numbers...

About the buttons: media player has nice buttons, would buttons of that kind be an alternative for you? Then the text would have to be part of the graphics, I guess.

Reija