There was a time when every office was an island held to others by the most tenuous of connections to the rest of the world. In this environment files and mail can only be viewed rapidly and conveniently by storing the files and mails within your own four walls.
For most small businesses who are not working with video archives or specialized applications there is now little need to operate a server locally.
File storage can be achieved both for shared and personal files via a cloud service called DropBox ($10/month for 50Gb) as well as others. The files are cached (That is, Local copies kept on the users machine) to achieve speedy access from multiple machines. Folders can be shared. This allows local editing tools such as Open Office (Free) or Microsoft Office ($149+) to be used locally with more effective window management as well as ‘cut and paste’.
E-mail can be provide from cloud or dedicated hosting by Clear Crescendo using IMAP and Thunderbird to provide access from multiple machines.
The leading accounting package is QuickBooks Pro ($159.95) and the other online offerings don’t offer the same level of functionality and integration, particularly for US businesses as the main online competitors are from other regions. QuickBooks does offer an online solution at ($9.95/month) with reduced functionality which at present offers the best solution. If the business is large enough to want to have multiple users within the office on different machines accessing the same QuickBooks accounts then it will be necessary to operate a server or for one of the users to play the role of being the server for QuickBooks.
Other than for specialized reasons most small businesses with less than ten office staff are not going to see sufficient benefit from operating servers on their own site and are better off configuring online services.