First up, if you use Twitter, Amazon is offering up a free $5 credit for Video-on-Demand (which gives you the option of renting movies to watch on-line or buying the digital version) if you link up your Twitter account with Amazon. I'm not sure what they'll do with your Twitter account, but as I have an account I never use, I linked mine up just for the credit (and may discontinue the link in the near future).
Simply go here and follow their instructions to receive your free $5 credit. Which you may want for a future deal.
