Twice, but all was OK. First time on the old CB, I parked in a buddy's gravel driveway and didn't ralize how soft it was. As I was walking away I noticed the bike start to lean and ran back to it. I grabbed it and eneded up pushing it over on it's other side. No damage I could see, as it's a '75 and beat to hell anyway.
The other time was last fall on the CM on one of those really cold mornings. There was a spot on one corner that had been wet for several days and I wondered if the city water pipes were leaking under the road. I came up to the corner to the stop sign and surveyed the situation. Water and slush all over the road about 1/2" deep. I thought I could handle it and headed through. I made the corner and after straighteneing out I looked down where the water was bubbling out from the road. I don't know if that unbalanced me, or if I hit a bit of throttle when I twisted my body, but next thing I knew I was spinning across the road following my bike. We stopped and I jumped up checking for traffic. A couple of cars had stopped, and so I immediately grabbed the handlebars to jerk the bike back upright. Right hand on the throttle and pull makes the engine rev, bike still in gear, standing on black ice all makes for an interesting time. The bike took off spinning around me as I scrambled to get my hand on the clutch or reach the killswitch. I finally got it stopped and pushed it to the side of the road. The car drivers were pretty wide-eyed by that point. Lesson learned: If (when) I ever drop one again, shut the bike off before lifting it.