The benefit of Hardware firewall is that hackers are most likely to be stopped before even entering your network. With software, hackers are able to get a little further in your network (passing your switches, hubs), and finding a specific computer to attack, hopefully finding a broken lock. Some software firewalls such as an OS (Solaris, NT, Unix) made for security and firewalling will act somewhat like a HWF by stopping hackers before they enter your network, and are just as effective as routers. A good thing about HWF is you don't have to worry about it going down once you set it up. Unless you lose power, but that would also mean your comp would lose power too, unless you are using back-ups.
I know a few running a Unix box and HWF, Cisco Pix, and Nokia FW-1. But I really don?t see a benefit to running ZoneAlarm and HWF at the same time. Personally, I feel HW and software firewalls offer higher or better MTBF. But HWF should offer higher MTFB because it's less complex to setup.