Google's Gmail service was inaccessible for several hours on Monday, inconveniencing millions of users worldwide.

In what is becoming an increasingly common ritual among online computing service providers, Google issued an apology.

"Many of you had trouble accessing Gmail for a couple of hours this afternoon, and we're really sorry," said Gmail product manager Todd Jackson in a blog post. "The issue was caused by a temporary outage in our contacts system that was preventing Gmail from loading properly."

Those with memories stretching back to early August may recall that Apple CEO Steve Jobs, in an internal e-mail that somehow slipped from the grip of Apple's message machine and reached the public, expressed regret for the rocky launch of the company's MobileMe service. "The MobileMe launch clearly demonstrates that we have more to learn about Internet services," Jobs wrote.

And in the even more distant past, July 20 to be precise, Amazon's Simple Storage Service (S3) was down for about eight hours. Amazon published a lengthy post-mortem of the incident. It concluded, "Though we're proud of our operational performance in operating Amazon S3 for almost 2.5 years, we know that any downtime is unacceptable and we won't be satisfied until performance is statistically indistinguishable from perfect."

What sets Google's apology apart beyond the inclusion of an actual "We're really sorry" is the extent to which the company's contrition appears to have been driven by engagement with its user community. Jackson acknowledged receiving not only phone calls and e-mail messages from upset Gmail users, but to reading complaints on Twitter.

According to Jackson, Google has identified the source of the problem and fixed it. He said that Google is conducting a review of the outage and plans to adjust its internal systems and procedures based on its findings.