I guess Amazon Cloud Front is the CDN then, rather than S3 itself! :) Whilst it seems fair to assume two UUID will almost certainly not collide, the way you po

I guess Amazon Cloud Front is the CDN then, rather than S3 itself! :) Whilst it seems fair to assume two UUID will almost certainly not collide, the way you pose that last question sums up my query: If your users don't want other people peaking at their files (DropBox): yes absolutely The answer is yes. Ultimately, users should not be able to see each others files, and from what you and other commenters are saying, UUID's on published files are still not robust enough to achieve this. Thanks for your information.