Matt’s post on cloud based software rental, and the article he links to, is worth a read but be sure to also read the comment it generated, especially from Kevin Quigley.
Dezignstuff SolidWorks Blog » You-bought-it-you-own-it vs the Cloud
Kevin Quigley: Matt this is a serious issue. I can speak from personal experience of this type of licensing via my encounters with Think3 in the early 2000s…
While the rent vs “own” (ignoring the “what is a license” debate) has it’s attractions there is a potential risk when you are talking about long term data use. The “reverts to a viewer when you stop paying” mode is not a solution when business critical information is locked up in that file. It was one aspect of pre-Autodesk “rent not own” Revit that I regarded as a negative.
It’s why I prefer the hybrid - create & save local/sync in cloud - approach of services like Live Mesh.

(Yes, this blog is hosted on a cloud service, and that image up there is coming from another, but I write nearly all the content off-line (saved & backed up locally) and there is a Export function in TypePad. It is just HTML content so rebuilding would be a mission, but not impossible)