well ive been on a 125 for the last two years. and that was a little wierd to get used to. but as with anything, just because itll do X speed doesn't mean you have to go that fast. you have all the control in the world.
yes i have stuffed it before. the metal in my knee will attest to this. has it stopped me riding? nope. it was a stupid mistake i made, toned it down a bit since then. i'd not like to stop riding though!