I've been down a few times. Both tips from Keith's second book and knowledge of friends having gone down and mistakes they made helped me survive both.
First was June 2010 at Barber, level 1 KCSS. Mid corner, S1000RR, everything was well under control, leaned over a little more, the next thing I knew I was on the pavement. Post crash analysis revealed nothing unusual by riders behind or coaches nearby. Could I have applied a bit of throttle while adding lean? Maybe. Usually the S1000 prevents that, but who knows. While I slid on the pavement, my helmet bounced (boy did that make for a headache after) and I remembered the "Crashing" chapter of the 2nd book. Don't move - stand still, let people pass you by, then when it's safe, exit the track. Did exactly that and avoided becoming a moving chicane and/or target. Lessons learned? Don't add throttle mid corner (already knew that but it may have been unconscious) and stay still after coming to rest. Also, keep your head UP, don't let it bounce!
Second was a couple months ago - mountain ride with friends. Got rainy/dark all of a sudden, began pouring, construction zone. DOT did not properly remove old stripe on road but instead painted over it in black slippery paint. As I crossed over to the new temp. lane, rear tire under maintenance throttle spun out and slammed me to the pavement. $1500 in cosmetic damage to my bike, one or two broken ribs, but no other issues. Remembered a buddy who crashed recently at a slow pace (20mph at most) and wrecked his leg. Shattered in multiple places, nerve damage, the whole bit. Decided to stay tucked on to the bike (touring bike - panniers triangulate so that bike doesn't crush your leg when it lowsides) until it hit the pavement, then let go. Kept head up, felt sore but fine. Rode 3 more days til I found out rib was cracked. Lessons learned? Tuck in for street crashes (if it makes sense). Kept head up - no trashed helmet this time!
Headed back to KCSS in August at my home track (VIR) for some more training. Always improving!