Site Office is something I've begun work on several times and then get side tracked. So far it is just a user interface and plugin model with no real working features. The idea in my grand vision of mojoPortal is to have everything you need to run a business built in or available including office like features.
I leave it enabled on demo.mojoportal.com and on mojoportal.com just to illustrate where things are headed. Many times web developers need to build business type web applications and they want a consistent application user interface rather than the kind of styled creative user interface we see on the public facing web pages. So while developers can currently build features that plug into the content management system, Site Office will be another option for plugging in custom features more geared to business applications where a consistent UI is desired.
Ultimately we will have things for outlook style email and private site messages and things for managing/sharing documents and calendars. Since it would take a long time to build features like Word, Excel, Powerpoint, accounting systems, we will build some things and do integration with google Documents and Microsoft Live. The final goal is just to be able to do every task related to running a business in the web browser and have it all tied together. This will allow collaborating with employees located anywhere. I envision more and more business moving to a model of having remote workers rather than paying for cubicle space and relieving the worker of related transportation cost time and stress associated with commuting to an office.
You can enable it by this setting in Web.config or user.config
<add key="UseSiteMailFeature" value="true" />
Best,
Joe