1) Proven Scale. Netflix. They're bigger than I will be until such time my company can afford to buy it's own data centers. At that point, I can re-evaluate. 2) Operational overhead. Startup, running hundreds of hosts, thousands of requests per second, 5 developers, 0 sys-engineers. 3) Lock in. We use Cloudwatch, Dynamo, RDS, Beanstalk, S3, EMR and more. We also use Heroku. No one else out there has the full suite of offerings. Not using AWS would require us to stitch together offerings from several vendors, some technology wouldn't be feasible having to hop across the internet (do you want the lag to get to your database from one data center to another?) 4) Billing. We get 1 Bill which we can predict. AWS takes credit cards, will do Net 30 billing, and are generally pretty flexible. 5) Customer Service. Don't get me wrong, support at AWS is ... not it's strong suit. We also don't spend enough to be a "big fish". However, if we used 10 different providers to get our infrastructure together, we'd me a minnow to each one. By consolidating, we're a small-medium sized customer which is enough to get into beta's, info on their roadmap ahead of time, and some personal service. 6) Excuses for downtime. So many high profile companies are on AWS that if we have an outage directly attributable to AWS, the odds are a lot of the rest of the internet is down, too. Seriously. It sounds stupid, but it's a huge reason. 2 years ago we were raising money. Right in the middle of our final week (when all our investors were visiting our site and making sure they really wanted to sign on the dotted line), we had an outage that lasted several days. This was the AWS outage that took out Heroku for a few days, and ours was one of the last databases to get restored. If we were using almost anyone else, investors might have been like "oh, this team doesn't really know what they're doing, they're not really that technically competent, I'm not going to invest". But since Netflix, Foursquare, and dozens of other companies were all offline at the same time, the investors were just like "they're using AWS, if Netflix can't keep online with hundreds of engineers, then I'm not going to expect that this little startup is going to do better". 7) Could I really do it better? Is anyone else doing better? AWS is the leader, so we all see the warts ... but at least they keep their certs updated (ahem microsoft)