OK, I added 'Like' and 'Tweet' buttons to display for each topic (just the first post rather than every reply). Unfortunately, the FB text doesn't show up on the dark background of this theme. It seems to be a problem with the code that FB returns, since it's setup to ask for light text on a dark background.
UPDATE: On second thought, I don't think the buttons are quite ready for prime-time, given the text color issues and variability with the links they produce (looks to me like every URL is unique, so the counts are wrong; i.e. two people clicking 'Like' or 'Tweet' on the same page won't show up as sharing the same page). In the interest of usability I've disabled this until I can find a better option.