Sometimes updating bios or drivers for network devices end up messing with the MAC address, and every cable modem I've used absolutely hates that. Powering the cable modem down for a minute powering it back up, and then rebooting either the router or computer seems to fix that particular issue.
Other than that... I don't use the built-in nvidia firewall or any software firewall because I'm satisfied with the security my router provides and I want a single place to make configuration changes. I'm also fairly satisfied with my own internal lan practices so I don't need/want a firewall on every machine within my lan to protect against attacks from within. That said, my wife's machine uses the standard microsoft firewall, but she's on a wireless connection and I want to at least try to prevent easy intrusion in case her computer ends up connecting to someone else's wireless lan for some weird reason.
