Amazon's affordable cloud-based EC2 (Elastic Compute Cloud) Web hosting service has attracted many popular startups in the social media space, and technical issues this morning have taken down several popular services including Foursquare, Reddit, Quora, Hootsuite and Moby. Amazon obviously has a huge online retail presence, but the company is also one of the world's leading cloud services providers -- startups are drawn to EC2's variable pricing model that lets them scale as they grow.