Gave out all but 1 of my cards to anyone who asked for them. I figure my odds are decent that at least a few of them will hit the 5 stays. If I didn't give them out at all, I'd have no chance, and most people I know personally are already SPG members or aren't the type of travelers to ever stay in a Starwood Hotel.
As for the bonus, in another thread on this board Starwood Lurker confirmed that you won't see anything on your account until 6-8 weeks after the END of the promotion (thus, don't expect anything on your account until mid to late September).