The hype about cloud computing has gotten so loud that Gartner Group used Cloud as the lead in its hype-parazzi special report Hype Cycle 2009. The sharply sloping graph in the report places cloud, along with e-book readers, wireless power and social software suites, at or near the "Peak of Inflated Expectations," preparing for a dive into the "Trough of Disillusionment."

One thing that may drive it into that trough — other than the unrealistic projections by some providers of cost-savings and easy capacity planning — is the difficulty in getting certain applications to run on it effectively, according to analysts and vendors selling technology to help bridge the gap.

What are the difficulties? Here's a look at five key hurdles.

1. Today's clouds are not alike

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"Legacy applications come with a lot of integration with your other systems, and usually they had to be done fast, so you have a lot of direct database calls from one application to another and that kind of thing that may not work when one endpoint is outside the perimeter," according to Golden.

"There's the tiny straw issue, too; there is an order of magnitude more bandwidth available inside the data center than outside it. And you have to decide whether it's important that you manage everything from one pane of glass, because the management tools are not up to doing that with cloud and legacy applications yet," Golden says. "There are a lot of basic technical issues that are often not addressed."

2. Security worries

Cloud Security: Danger (and Opportunity) Ahead

"For enterprises that have security or compliance concerns, multitenant cloud infrastructures are just non-starters right now, because the tools to monitor or control that has not been addressed yet," he says.