I good concept, but realistically it has already been achieved, maybe not in the same way, but close to it. Think of Google groups,basically it is like share point services. You can chat with members of your group, get access to Email using Gmail and use Googles online apps, like its version of word, excel and so fourth, which can be posted and accessed through the google groups module. I think the real benefit here is no piracy, which works in Microsoft's favor and in the future will probably eliminate it, when and if they go all online with there office software suits. Realistically I think it won't work to well especially in country areas, where Internet Infrastructure doesn't have the best reliability. Relying on an Internet connection alone for any Business is a risk and some can't afford down time and that is where Microsoft can't guarantee the up time. Personally I wouldn't out lay IT support to Microsoft or any other online resource, simply because you don't know who has access to it or controls where the data is kept and you can't be certain that backups will occur and will restore properly if a disaster does occur. A cheap and cost effective option is definitely correct.
Cheers
Prim