Big tip of the hat to The Frequent Miler. I've mentioned American Express' "Sync" offers here before. Amex frequently offers some really great discounts (in the form of automatic statement credits) for places that I regularly shop. For instance, they are currently offering $10 off a $50 purchase at Lowes. The trick is that the Amex website will only allow you to sign up for these offers for your primary user card. If you want to sign up authorized users, you need a work-around.
Twitter works great for this because if you sync an Amex card to your Twitter account, you can sign up for many of the Sync offers by tweeting a specific hashtag (#AmexLowes, for example). The trouble is that you can only sync one card per account. So naturally, I set up 8 different Twitter accounts for each of my primary and authorized user accounts. There was still a bit of effort, but in a matter of minutes, I could sign up every card I controlled for any particular Sync offer.
I thought I was being very clever, but some others had me beat. As TFM points out, you can use TweetDeck (a Twitter service) to send out identical tweets from every Twitter account you control! That means one sign in, one tweet, and you can sign up 8 (or 10 or 12) Amex cards for any Sync offer that's available on Twitter. Sweet!