Just a quick note really. I have finally got round to starting off my Wiki page on the use of automatic proxy configuration files. I decided to write this mostly so I wouldn't forget in future but also as I found .pac files to be really useful and thought others might want somewhere to start when first implementing them.
So, if you want to make your proxy infrastructure more resilient, or just move those annoying proxy exceptions somewhere other than people's NT profiles, then give a proxy auto configuration script a go. That way if you have to change the exceptions list, all your users have to do is restart their browser to pickup the new settings rather than logout and in again.
If you are feeling really adventurous you can even do things like send users on different network to different proxies, send users to different proxies at different times or route through different proxies based on the protocol of a request. The possibilities are endless.