I've not tried it myself(at least, not often enough to have useful data), but from all I've heard it can work. It's low probability - single-digit percentages for most guys, it seems - but the investment of time and effort in doing it is sufficiently low that it can still be a good strategy, as long as you have a high tolerance for rejection.
P/S/A: There are single sentences which can create life-changing amounts of difference.