office doc / spreadsheet intergration
Apple Mac OS X Server
Outsourcing solutions like windows live and google apps can save you money but put some else in control of your data. Googles solution has the best promiss right now. Microsoft still has not added all the extras needed to compete with google. Microsoft has also changed how the technology works many times in the last few years. Google seems more stable and dedicated to maintaining a stable platform. Exchange is still number one for the current future and with exchange 2007 claiming to be able to scale without the need for hundreds of servers it might be the case. If you can afford it exchange 2007 may be a good choice. One of the problems with exchange is they have not decided on what to do with public folders. They seem to want to have everyone move to sharepoint which just became usable. They have changed the IM solution on each version of exchange. All the apps to make up the exchange group solution are not very coordinated. The google soultion is still a work in progress but the single signon and the way the apps hinge on the email framework is a very good technology. If I was a small business I would not take a moment to pay google for the sla version and maybe dump windows and microsoft office all together. Might be something to look into.