I hope all the newbies read this. This usually happens whenever there's a large inflow of new users to any social network getting popular. I remember getting Facebook friend requests from people I didn't know, and seeing a ridiculous amount of "kfb"(kindly follow back) tweets on Twitter. As Steem grows and matures this type of behavior should (hopefully) dissipate.
RE: Following back, spam comments and... OK, dear new steemians, it doesn't work like that!