I have a 5.6 installation that is a file server and serves up web pages from user directories for students at our school. We are a laptop school and the server sees hard use. It is the only network storage for student files and they are using the web pages for projects, etc. It is used as a proxy/squidguard box sometimes when the primary machine is down.
We have over 800 accounts, and all the clients are win 2K.