I put the PC III USB on my '03 Ultra. I'm set up with Vance & Hines, Big Bore Stage II w/SE 203 Cams & SE Air filter. I had a lot of popping and backfiring almost anytime I let off the throttle, like coming off a highway onto an exit ramp, etc. Love the V & H pipes, and tons of pull, but the bike was definitely running too lean.
After putting the PC on the bike and downloading map M807-096.djm, I also turned on the accelerator pump feature with 90% sensitivity and a 15% fuel increase for 20 RPMs, which seems to be suggested for street riding.
I went out for a 50 mile ride (in 40 degree weather - that's desperate!).
Bike runs great. I still get the occasional carb fart, but the bike runs great, no hesitation or issue at all. Now I only went 50 miles and since then it's been crap weather here in New England, but I was happy with it. I jumped on it and went to 110 for about 20 seconds and was very happy with how fast It got there. Can't find a downside. I researched the PC for a while, mainly through sites like this. I'm sold on it. I plan on putting it on my '05 SEEG this winter.
JRW