If your band has a myspace page (and it should!), you can send out notices of your upcoming gigs / events to your list of friends. Of course you have to get all those friend invites done, but once it builds up, people will find
you and you'll have a list of at least semi-interested myspacers that you can spam repeatedly
My bud and I were talking about this last night... he has a pet peeve about getting a myspace notice from certain artists that lack the more obvious details. E.G. he got one from Ray Wylie Hubbard saying, We'll be at Martha's again this Friday! We're down here in FL, but have no idea if Martha's is in Texas, Maine, Seattle, or Florence SC
other than that it's a pretty cool tool