Amazon’s infrastructure services, which include Simple Storage Service (S3) and Elastic Compute Cloud (EC2), have been used by several online backup startups, and have gained raves from several early users. These include the photo storage site SmugMug, which says it has saved $500,000 by using Amazon for storage, and the virtual world Second Life, which used S3 to deliver 900 gigabytes of software downloads for less than $200.

But the S3 service has experienced growth-related performance problems, and Alexa’s trouble this morning provide a reminder that even Amazon’s mature services are not immune to downtime.