SBS is easily one of the best things MS has ever created. It allows small businesses to have all the Enterprise stuff without the Enterprise price. It is also easy to set up and maintain making it highly cost effective.
Tom,
One of your first ventures into Sharepoint should be, I recommend, using the vacation calendar. I know that sounds trivial, but it has helped our office tremendously and is a good starting point. Also, as Bert said, go to Godaddy and get yourself a domain and cheap SSL cert and you're good to go with having your own Exchange environment.
SBS is also easy to extend. Since you have Exchange and assuming your office does tons of faxing, you can look into Faxmaker by GFI (
www.gfi.com). We use Faxmaker to route faxes to the appropriate employee via caller ID. Very handy.
Resources:
The Official SBS blog:
http://blogs.technet.com/b/sbs/The SBS "Diva":
http://msmvps.com/blogs/bradley/default.aspxJamesNT
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