The estimates for cloud computing can make you wonder sometimes about what to believe. Analyst firms and it looks like investment houses, can be notorious for wild estimates about market sizes.

So we have to wonder about the estimates from Merrill Lynch, which is estimating the cloud computing market to reach $160 billion by 2011.The estimate includes $95 billion in business and productivity applications.

Whoa! That makes cloud computing one of the fastest growing markets in the world.

But Merrill Lynch is not alone in its lofty estimates. Earlier this year, Gartner pegged the market at $150 billion by 2013.

In their estimate, Gartner included Google Ad Words estimates in their estimates. This seems sketchy at best. Here's what Gartner analyst Lydia Leong wrote back in May:

"Obviously, one argue whether or not it's valid to include advertising revenue, but a key point that should not be missed is that in the trend towards the consumerization of IT, it is the advertiser that often implicitly pays for the consumer's use of an IT service, rather than the consumer himself. Advertising revenue is a significant component of the overall market, part of the "cloud" phenomenon even if you don't necessarily think of it as "computing".

What's at risk is making cloud computing totally irrelevant. How can corporate IT departments make sense of the market when it appears that cloud computing is essentially tied to anything connected to the Internet?

But then you need to look at the dynamics in play. IT is built on legacy systems, custom, built to order environments. Cloud computing provides a level of automation.

From the PriceWaterhouseCoopers summer Technology Forecast:

"Legacy IT soaks up much of the available IT budget and is a primary barrier to IT responsiveness and overall business agility."

The report goes on to say that cloud will be necesssary for automating the world of IT:

"...IT must adopt an architecture that creates loose coupling between the IT infrastructure and application workloads. It also must modernize and automate IT's own internal business processes for provisioning, managing, and orchestrating infrastructure resources."

In other words, cloud computing will be huge but to call it a $160 billion market seems like a form of hype that can lead to all kinds of issues. It's almost reminiscent of the dot-com bubble.

And look what happened there.