I have recently setup a Linux server to begin serving a small (12 users) legal firm that had Windows Small Business Server 2003 running. The issue was that they were not doing anything special, just FILE SERVING, and so a Linux/SAMBA solution would get them away from needing anything in the way of a proprietary server...
So I took a good look at the config details, crossed my fingers and went for it - and was very pleasantly surprised ! It was a simple task, and I have since found the software to be very stable, very fast, and easy to maintain.