The linux machine grew with his business, and was only recently replaced (due to a motherboard failure). When I asked him what kind of OS he wanted on the new server, the choice was clear: Linux. Since it requires so little maintenance (none from him and only remote administration from me) he's been one of the most vocal Linux advocates in the small business community, and had several business in our area come in to see how well Linux works with their existing technologies.
Did we have trouble? Yeah... ACT didn't like to be on a SAMBA share (until I found out it needed oplock tweaking), and getting tech support from his ISP was troublesome, but once everything was set up, there was nothing more to do.
Small businesses often can't afford to have a full time IT person, so this kind of set it and forget it proposition makes great business sense.