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Update: HostedFTP.com - Amazon S3 Performance Report. How fast is S3? Based on their own study HostedFTP.com has found: 10 to 12 MB/second when storing and receiving files and 140 ms per file stored as a fixed overhead cost. Update: A Quantitative Comparison of Rackspace and Amazon
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Photobucket's free account has a storage limit and a download bandwidth limit of 10 GB per month. There's no bandwidth limit on the $25 Pro account.
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Flickr offers a free basic account with limited upload bandwidth and limited storage. Download bandwidth is unlimited. Upgrading to a paid Pro account for $25/year removes all upload and storage restrictions. Flickr's terms of use warn that "professional or corporate uses of Flickr are prohibited"
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ImageShack offers free, unlimited storage with a 100 MB per hour bandwidth limit for each image.