Canonical had earlier announced plans of shifting Ubuntu's repository archives to Amazon cloud in order to provide better services to users. The good news is this is finally done and users will now be able to download packages and updates right from Amazon S3.

Ben Howard, Software Engineer at Canonical, announced in his blog, "On June 13th we announced that the us-east-1 region has been switched over to S3. As of July 5th, 2012, all remaining EC2 regions have been migrated to S3. The immediate effect of this change is that AWS VPC instances will no longer experience bug 615545 and will have access to the default selected Ubuntu mirrors."

Micro Warning
Due to a bug in S3′s HTTP implementation, users may experience 403, 404 and 416 HTTP errors during update or installation in some EC2 regions.

Ben says, "Notably, Ubuntu 11.04 users will see 403 errors while updating the apt meta-data and Ubuntu 10.04, 11.10 and 12.04 users may see hashsum or size mismatches."

If you face some errors while downloading packages or updating archives, it is advisable to disable http pipelining in apt using the following commands:
$ echo ‘Acquire::http::Pipeline-Depth “0″;’ |
sudo tee /etc/apt/apt.conf.d/99-no-pipelining