Whilst the win7 firewall is better than previous incarnations of the windows firewall, the outbound protection is disabled by default, that should be enabled.
Any malware that manages to get past your defences will have free reign to connect to the internet (and not all malware comes from the internet) to either download more of the same, pass your personal data (sensitive or otherwise, user names, passwords, keylogger retrieved data, etc.) or open a backdoor to your computer, so I believe outbound protection is essential.