Since you really can't have too many cups, you might as well add the Twitter Friends Mug to your collection. If anything, think of it as one of those 'friends' you follow on Twitter. If it doesn't work out, or you don't find it particularly interesting, you can just unfollow or get rid of it.
Of course, for $15 you may not want to get rid of the Twitter Friends Mug. And really, why would you? It's a rather simple process as well. Simply type in your Twitter username at Crowded Ink and it'll automatically compile those pretty profile pics for you.