http://www.appleinsider.com/articles/09/10/24/inside_apples_new_mac_mini_server.html&page=1
Not for everyone but could be very cost effective for small businesses with 10+ employees.
Certainly fills the void for small businesses at a price that small businesses will like. I think that's the first time I've looked at an Apple product and not thought that the price was out to lunch, either.
The one thing I didn't glean from that article was whether Snow Leopard Server interoperates with Windows clients.
- File services (SMB yes)
- Mail services (imap yes)
- Calendar (caldav yes)
- Open Directory account managment.... needs more research from the sound of it maybe.