I'll start with a simple newbie question. Suppose I've got, say, 100 keywords I'm bidding on (using very specific long-tail terms, of course), and I want to evaluate them to figure out which ones are converting, and which ones aren't. How many hits do I need to evaluate a given keyword? If it's not converting after 10 clicks, that's obviously too small a sample. But what about 100 clicks? 1000? When should I give up on a term, and when should I just sit and wait?