For personal PC firewall use I currently use 2. And I change them often. I was useing Zone Alarm and Black Ice, untill I noticed a CNN news artical about Black Ice actualy letting hackers get into you computer easier than without it. I have gotten the new pach and am currently useing it again.

I find that if I keep at leat 2 Firewals running that one will block certon intruders and the other one will let them in or visa versa. What I try to do is keep up to date on the new updates and patches on diffent versions to keep my chances of getting hacked down.

I prefer to run firewalls that are some what specific in their task like Zone Alarm is a appliaction bassed firewall, while black ice are more packet watching type of firewalls. I have to admit Sygate, is one that has alot of features that I like, it also uses applictions and packet types in one.

I have not found much info about running more than one on a pc. but I feel more secure than not by doing so. Most people that I have talked to about it seams to thinke there is no reason to do so. but what I have found is that if some one fines a exploit on one of then they are less likley able to get through both of your firewalls.