my experience: most (not all of course) are price shoppers, wanting a price over the phone and then they compare it to the other 3 fellas that call them. if you are a good salesman (i'm not), then you can do better, if your focus isn't low price. if your biz is all about low price, you could do well.
since we joined in June, we've had about 24 leads. at least 2 they deemed bogus and we were credited.
since i don't focus on the lowest price (or maybe the fact that i am not good at sales), out of 22 legit leads, i only closed and CC'ed for 1.
last year's leads cost $11 per. this year i think it jumped up to $13 per.
since June, with the $99 join-up fee, S.M. has cost me $345. i've made $787.42 from them.
bottom line: i think i got fortunate to have found 1 client who is not focused on price, but still i wouldn't recommend S.M. to anyone.
if you do join, your best bet is to work hard on your S.M. website and make it stand out (learn some basic HTML).
hope this helps. thanx --- Derek.