What do you think the difference is between a good spotter and a bad spotter?

Once time while benching I asked for a lift and the guy threw the weight at me. He threw it so hard it almost got past that point where it would have come crashing down on my legs because I wouldn't have had the leverage to stop it.

I think the key to being a good spotter is to ask the lifter how they want to be spotted. If they start to fail do they want a little help, like two fingers under the bar, so they still have to struggle to get it up? Or do they not want to work through failure (powerlifters may tend to feel more this way than BBers) and just want your help as soon as the fail? And when to help needs to be discussed, too. I hate people who help me lift on every rep, so I try to remember to say "don't touch it unless I say 'help.'" A good spotter realizes that it is the lifter's set and not theirs, so spot how the lifter wants it.

And I think one person spotting on squat from behind is rediculous. The squat is such a technical lift that even if the person did help it would completely throw off your balance and center of gravity and possibly cause you both injury. IMO, the only way to safely spot on a squat is to have one (or more) people on either side who lift the ends of the bar. Of course, then you have to make sure they lift at the same rate so you don't tip over. You don't have to worry too much about this, tho, if you use the safety bars in the squat rack

So what do you hate and love about spotters, etc.?