I push my dirt bike up a dual ramp while walking beside it on the ramp. For larger bikes, under power in first gear, smaller bike get manhandled in. I always leave the bikes in gear when backing them out so I can drop the clutch if the front wheel starts sliding on the way down the ramp.
I used to ride up the ramp. No problem after a ride when I was fully comfortable on the bike. Different story first thing in the morning with a cold bike, cold body, and pretty much no gear.
I used to make my sister load her bike by herself all the time (in case I was ever incapacitated and she had to go get the truck, she would have practice). One time she loosened a strap too quickly and the bike fell, knocking her out of the bed of the truck, except for her leg that was pinned. Another time as she backed the bike down the 'ladder' type ramp the front tire started sliding (she didn't have it in gear) and she stepped through the ramp, bike fell on top of her, general bad scene (wish I had that on camera). Despite some pretty major scrapes and bruises, and a big dent in her shin, she was still up for the all day ride we had planned.
2008 BMW R1200 GS Adventure
2000 Honda XR400R