Here's my experience setting up a Ubuntu client to print to a printer on another Ubuntu box:
Printer server (IP 192.168.1.6) is Ubuntu Karmic 9.10 with HP 5550 on USB port:
Printer client is Ubuntu Karmic 9.10.
Modifications to etc/cups/cupsd.conf on Server box:
1. Adding "ServerName 192.168.1.6" doesn't seem to make any difference.
2. In the Listen section you must add "Listen server-ip" after "Listen localhost:631":
# Only listen for connection from the local machine.
3. You must add "Allow" for subnet in Location section:
# Restrict access to the server...
Allow From 192.168.1.*
Restart CUPS after making changes to cupsd.conf on the Server box.
I found that you must add a /etc/cups/client.conf file on the Client box to point to the Server box:
Restart CUPS after saving /etc/cups/client.conf on the Client box.
Now, if you try to print from an application in the Client box, the printer should appear in the Print dialog box. No need to Add Printer.