You may find the next post interesting (coming soon), we’ll be discussing the “hidden” agenda behind cloud computing, however at present and in answer (partly) to build scenarios….

A bespoke TMG solution would be tailored to work with a combination of existing “best of sector” solutions to provide the most cost effective platform for the clients needs, depending on what they may be. There’s still a definite place for browser based local groupware suites such as Citadel (see previous post). Bandwidth around the local LAN is free.
For example, a classroom tutorial suite (or similarly dynamic environment – e.g a cyber cafe) would most likely be a mix of LTSP with basic web access dependent on the chosen (most affordable ) web link available and maybe even some “fat” clients, a small to medium sized business however would push a Google Apps scenario with options for local storage if preferred.
“Storage” needs mentioning here as it’s different to “backup”. Backup is a misconceived term which actually should have no place around the cloud due to bandwidth considerations (i.e any bandwidth costs money). Data should either be up or down (in the cloud or out). Store it locally and back it up locally or store it in the cloud where integrity is taken care of by the host, moving it around unnecessarily will just incur equally unnecessary cost.
So, a class of students? It probably would have no need for total cloud cover, and a business enterprise? They might (and could), if it was financially viable (and we are talking about today, not tomorrow), but to be honest even with a generous view toward future developments it would still be advisable to be functionally selective.