As the economy crumbles around it, Amazon.com yesterday reported fourth-quarter financial results that blew past Wall Street's expectations. And, though details are sketchy, it appears that Amazon's cloud services grew at nearly double the rate of overall sales.Amazon reported revenue of $6.7 billion for the fourth quarter of 2008, an 18% increase over the same period a year ago. Highlights included a 31% increase in international sales (excluding the unfavorable impact of foreign exchange rates) and a 31% jump in worldwide sales of electronics and general merchandise.

Yet, even those impressive numbers were overshadowed by the part of Amazon's business that includes Amazon Web Services. Unfortunately, Amazon doesn't break out AWS revenue separately, though it should, and it will come under increasing pressure to do so. What we know is that AWS sales are included in a category called "other" -- included are AWS, Amazon Enterprise Solutions, co-branded credit cards, and miscellaneous marketing -- and that overall sales in that category totaled $175 million in the quarter, a 34% increase over a year ago. For the year, Amazon's other revenue was $542 million, up 42% compared with 2007.

It's impossible to know how much of that half-billion in revenue for the year was generated by AWS, but it's clear that financial analysts are paying close attention. When Amazon opened yesterday's conference call to questions, the very first question asked of CEO Jeff Bezos and CFO Tom Szkutak had to do with enterprise adoption of AWS. Their response: "We think this is a very significant and meaningful opportunity over time for enterprise level customers."

It all leaves the impression that Amazon's EC2, S3, CloudFront, and other cloud services are a big success, but there's too much wiggle room in the numbers to be sure. We don't know if Amazon Web Services are growing at 10% or 100% because the details are obscured as Amazon reports them.

Amazon is notoriously cagey when it comes to the nitty-gritty of AWS. For example, it refuses to disclose the location of its data centers. If Amazon is serious about the enterprise market, it's going to have to get more granular in the information it makes available.