Facebook's 'young' and 'technical' performance requirements must be off the wall ;)
For the vast majority of apps, the latency will not be an issue. Especially since S3DFS has caching built in.
A good example is SmugMug who switches over to use S3 to serve out images when they are working on their own datacenter. Don McCaskill (their CEO and head programmer) says that switching back and forth was completely transparent to their users with no human-discernible latency. For more, see:
For the vast majority of apps, the latency will not be an issue. Especially since S3DFS has caching built in.
A good example is SmugMug who switches over to use S3 to serve out images when they are working on their own datacenter. Don McCaskill (their CEO and head programmer) says that switching back and forth was completely transparent to their users with no human-discernible latency. For more, see:
http://blogs.smugmug.com/don/2007/03/08/amazon-s3-the-speed-of-light-problem/
http://blogs.smugmug.com/onethumb/files/ETech-SmugMug-Amazon-2007.pdf