There is some potential for the Slice Of Pi to move and short against one of the components on the pi, though - I don't have my pi in front of me to check exactly which component that is, but it's in a round metal package. I wound up doing two things to avoid any problems :
- Put a small sticker on top of that component
- mounted the IC I was using on the underside of the board, so its plastic package would be the thing that came in contact with the component on the pi board.
Other than that, it fits over a mostly empty area of the board, near the raspberry symbol, so there's very little other risk of problems.
I'm really happy with the Slice of Pi - I just bought my second one, after making a "motor controller shield" with the first one. I haven't yet tried using the XBee support, although I plan to rectify that soon.