Get your suspension set up properly is IMHO the first and best mod.
Dave Parkinson at SP racing is in Southport and Andy White at KAIS in Atherton is only 20 miles away. Both come highly reccommended.
Its not always neccessary to respring or revalve, just decent setup.
My SPS came set up really wierd, set up for a 7 stone rider rather than a 17 stone fat git
and was transformed with an hours work.
Also Dukes tend to be overgeared and its a very common mod to lower the gearing.
Gearing and suspension mods are cheap and easy before you start on the Ducati disease of spending lots of wonga.
After that its the obligatory Termis and a FIM chip to improve the fuelling.
Oops nearly forgot, get brake and clutch levers set at right angle and helibars improved riding position for me, what i'm trying to say is get the riding position as comfortable as possible so you can relax and concentrate on riding.
THEN SPEND LOADS OF MONEY
[Edited on 3-8-2004 by BDG]