There's the obvious stuff like programming door-lock, interior light, and seatbelt-warning settings. More functional possibilities include turning down/off the EGR flow on ALH engines (and possibly 1Z and AHU motors too? definitely not PDs though). Coolest thing I've run across is the Passat tranny recode. That simple little modification, which took all of 45 seconds to perform, has singularly made our Passat 100 percent more pleasant to drive--the transmission now shifts like it's in telepathic contact with your brain. I have not once caught it in the wrong gear since the recode. Beforehand, you had to either use tiptronic or cuss at it all the time for holding the engine at 3500 rpm (remember, this is a DIESEL!) for absolutely NO reason.