If the graphics for a song don't exactly line up with the audio, you can slip the graphics into the past or future with the Sync-Slip commands in the Control menu. Slipping back moves the graphics into the past, slipping forward moves the graphics into the future. (The audio just keeps playing without interruption)
Each song permanently remembers it's slip value, so once you set it, you can forget it. You can show the slip values for all songs with a Context Click on the sort column headers, and picking "Slip" from the popup menu. Slip values are in seconds and the default increment is one tenth of a second.
There is also a Global Slip value, which is applied to every song (in addition to any Song Slip value), so if you are for example playing audio thru USB speakers, or over the network or even to AirTunes (using AirFoil) you can adjust the video to sync with it perfectly.
When exporting to QuickTime, Song Slipping is preserved, but Global Slipping is NOT applied.
When burning discs, NO slipiping is applied. (this is dumb, i know, please request it if you need it)
When editing with Producer, NO slipping is applied at all, so to see the song WITH your slip settings, you must exit Producer.