I've had an '03 Katana 750 since 2008. I bought an '01 in the spring to use as a parts bike but it seemed to run and sound better than my '03 so I flipped it. The '03 is now my parts bike.
I've added:
Denali Sound Bomb
Denali Power System
Heated grips
USB charge ports with voltage meter
2nd set of winter tires
LED headlights
Bark Busters for winter
58L Givi top case
48L side cases (with custom mounting racks)
Interior lighting for all 3 cases (Ignore the pinched wire in the photo, that's been corrected)
Power cord for heated helmet
Coming soon; backup lights (for the dark winter mornings and evenings), custom decals in the spring.
The carbs have received the GSXR jet kit. From what I understand the jets and exhaust are the only difference between the Katana 750 and the GSXR 750.