XBMC - Performance Issues?

I’ve noticed since installing XBMC that the client seems to be a little laggy, and suffers from constantly buffering the video. The AppleTV is connected to wifi using a Wireless-N 5Ghz. connection connected to a NAS through a Gigabit connection.

Any way of improving the memory footprint of XBMC, or is there a skin that can be installed to improve performance over the standard skin?