Much the same as friends and family above, however, the big difference, close friends and family (as mentioned above) one can actually call or see at home tonight for instance, so its harder to get away with saying you did do something if you didn't. Facebook friends, or any other social network friends you're not particularly close to in real everyday life, might not be as inclined to help out as a test subject for your new venture.

The upside to this is that although fewer people are likely to participate in your schemes, percentage wise, there are so many more friends one ould make on facebook or any other social network than you could in your normal day to day life, so you're potential "Mailing list" as it were could be infinitely bigger than that of your list of true friends and family! I say use 'em both! I do.