If the bar ends up in the right spot, you're probably doing them just fast enough. Ignore the weight you're using, focus on keeping the technique solid.
Dan John recently said to shoot for having your clean, flat bench, and front squat "pretty much" the same.
Hells yeah, man. They're such a monster move, that if you work them hard enough, you can do almost whatever you want afterwards. If you hit cleans hard, and follow up with smaller back or shoulder work, you'd be golden.
Rep-wise, I agree with Muppet and Oklahoma. I'd keep the reps anywhere between 1 and 4 per set, any more than that and cumulative fatigue will likely send your technique into the crapper. And vary your sets according to your goals. With that said, I was recently playing with cleans for 8x8. (Albeit with a lighter weight, and much shorter rest periods.) When I mentioned this workout to Dan John in his locker room thread recently, he gently suggested that it may not be the best application of the exercise. After a few workouts, I tend to agree. It helped my technique some, but probably no more than lower-rep, more frequent work would have. Plus, my grip was a significant limiting factor with higher reps.
One neato clean variation I've used, especially outside this past summer, was walking cleans. I'd clean the bar, take 2 or 3 steps with it in the rack position, lower it, clean it back up, take a few more steps. I'd do it up and down my driveway, about 80' each way. 2 tons of fun, definitely.