Although you might build say, a Sharepoint infrastructure in Windows Azure and leave it deployed as a permanent feature, totally integrated into your enterprise infrastructure, there are a growing number of organisations taking advantage of the temporary nature such infrastructures can have. Whether they need temporary access to a fully functioning IIS infrastructure, SQL infrastructure, AD infrastructure, System Center infrastructure or even a fully functioning, full-fidelity instance of one of their home-grown LOB enterprise apps - they can all be "popped up", used, then "popped down" again.
Whether you're an independent consultant who needs to replicate a problem at one of your clients, a small business that needs to run a training course for its employees or a large multi-national corporation that wants a dev/test environment that exactly mimics their production environment - pop-up labs can provide these services.
This video explains how in some cases, fairly extensive pop-up labs can be deployed for free and shows how they are so economically viable because they are only paid for when they are "popped up".
You'll see how to use Virtual Networks, Windows Azure Virtual Machines and Cloud Services to build your own pop-up labs.