Just who uses Amazon Web Services?

For some reason, I believed it was only the open source startup companies that took advantage of the incredible services offered by Amazon's Web Services, like the S3 storage service, EC2 compute cloud, and SimpleDB online database.
I mean, it's a no brainer - you want to server up your open source projects, products, why build a data center to host this stuff? Just give it to the S3 service and you're done. It's hassle free, and i've seen several of the companies i've been involved with select this over everything else out there. I had no clue that large companies, who have massive data centres with lots of $ invested in them, are also choosing the AWS services for many of the same reasons startups do.
This article by TechCrunch has a nice writeup and some insider information from Amazon which suggests that a lot of the AWS users are in fact Banks and other stogy, conservative outfits. Who would have guessed?
I imagine that this will become a major source of revenue for Amazon as time goes by, and I also bet sometime not to far from now, large companies will totally outsource a lot of their data centre needs to AWS as it becomes 'safe' and accepted to do so.

UPDATE: this story from Wired has some good insight into the AWS business and how it all got started. Great reading.
http://www.wired.com/techbiz/it/magazine/16-05/mf_amazon?currentPage=all