I'm bored, so I wanted to add to a really long thread that was solved ages ago...
1.) My CL350 does not have a kill switch and it's never been a problem. I don't even miss it. Then again, I hardly ride it.
2.) My RD400 has a kill switch. A couple days after my vasectomy, I decide a little bike vibes might be good for the nuts. So after kicking the bike for 10 minutes, my nuts are swollen to baseballs (exaggeration) and I realize my kill switch was off. Nice.
3.) On my Harley, I always use the kill switch to turn the bike off, then the key. But it has a weird start process due to being fuel injected.
4.) Before I started riding, I saw some douchebag kid let the clutch out too quick. He popped a wheelie, then went tumbling about 8 times w/ bike through a barbed wire fence and into a field. I turned the car around to help him and knowing nothing of how bikes worked, looked to kill the engine and quickly found the kill switch. I had to lift the goddamn Katana off the kid's chest (he was concussed)
So after all this, yes, kill switches are a good idea.
--Chris