In reply to Joshua :
The only mapping weirdness I've experienced has been the occasional "snap throttle closed/pull clutch in from medium-high RPM" stall, almost like the revs fall too fast and the ECU can't catch them in time once it realizes a stall is likely/imminent, but that seems to have mostly gone away with a map change (I believe the factory map for the Akrapovic slip-on was flashed to an otherwise stock bike, richening it up everywhere). Other than that, it's been riding fantastic!
In reply to secretariata :
After ~4800 miles, I've found it to be a very very competent bike up to about 80mph, above that it starts to become evident that I'm a 250# dude on a 372cc bike 
It'll happily cruise at basically any speed it can attain, although once one starts to knock on "major points on license/possible jail time" levels of extra-legal speed, just maintaining speed requires nearly 100% throttle. Gearing from stock is pretty short, to the point that first gear is more or less useless unless you're riding VERY spirited and are coming out of a really tight turn, or are trying to do wheelies. I installed a +1 front sprocket about 2000mi in and it makes a big difference. First is useable to around 25-30mph now, 2nd to just under 50, and 5th feels about as flexible at highway speeds as 6th does on a stock bike in terms of passing power. By gearing, it should top out at ~109-110 at the rev limiter in 6th, but I've got just a little bit too much internal ballast to properly test that theory 
Handling wise, I'm probably not the best person to ask, as it is my first bike and I'm only just getting proper "spirited" cornering technique dialled in as something I do subconsciously, but thus far I haven't noticed the bike having any bad habits. It seems well damped/well sprung for me, so someone who was a bit more proportional to the bike might find the ride to be on the stiffer side. My one quibble with the suspension is that the fork isn't adjustable at all, not even for preload, where at least the shock gives you that option. Preload adjustable top caps are available, as are fully adjustable cartridge kits (the Duke 390 shares the fork and shock with the RC390, which is hugely popular in Superstock 300 racing at basically every level, so the Duke ends up benefitting from that aftermarket as well as the RC390), but it is something I wish KTM had included from the factory.
The brakes are phenomenal from the factory, for even spirited street riding I haven't felt the need to do anything other than adjust the levers to my preference. Once I get the bike on track (first track day is at NCCAR/NCBIKE in early April) that assessment may change, but for the time being, the factory brakes are fantastic, with great initial bite and plenty of power from the front. The rear brake is fairly spongy and useless feeling, unsure if that's due to the amount of flex line in the rear brake system (front/rear ABS makes for longer than average brake hose) or a MC piston on the small side, or the simple fact that the rear caliper is of the single piston sliding variety and the caliper itself probably isn't the most rigid thing in the world. The rear brake does have more power than the rear tire has grip though, as when playing around in a parking lot getting a feel for ABS panic stops, getting rear ABS to engage wasn't tough.
Ergonomics wise, the bike is on the compact side of things. I'm 6'1 or so with a 34" inseam, and I feel like the bike is right on the edge of being too small for me to comfortably put a ton of miles on in a day, especially from the waist down. It is definitely rideable for someone my height/build though, and the riding position is pretty fantastic for control when getting after it a bit on twisty roads, without being too aggressive to be comfortable on the street.
