I get spam requests from Facebook all the time, nothing to do with here.  I don't do the Facebook thing, but have family that does.  That alone is reason enough for me to stay away from any of the "social" specific sites.  I love my mother, but I really don't want my entire family all up in my business. 

As for the friends thing on here, I only ever accept those requests if they are someone I know already, or have at least had -some- kind of interaction with here.  I have no qualms whatsoever hitting the decline box, have done so on several occasions, and will continue to do so no matter how many times some random person tried to "be my friend".  If you enjoy someone's art, watch them or fav them whatever.  At the very least, send them a note initiating contact that way.  It's like playing my MMO's and having random group or guild invites from someone who hasn't even sent you a tell.  If someone has problems being declined when they've made no true initiative to truly become someone's friend, well they probably have bigger issues than I'd wanna deal with anyway.  Just my opinion anyway.