Hi,
Web Shield is indeed using the same transparent mechanism that appeared firstly in avast 4.5 for Mail Scanner. So the same will apply: simply start the provider and you should be protected, stop it, no reconfiguration and you are again with your bare internet. For localhost proxies, the communication between the proxy and the outer internet will be scanned. Other configurations would be also possible - but that would require setting the proxy server in your browser or in your present localhost proxy.
Concerning the delay - well, there would be apparently some small delay - the payload needs to be scanned and that takes some time. But the scanning process is optimized for this kind of usage and the networking stuff is also optimized for high throughput, so hopefully you will find it very quick or better not noticeable at allĀ
We might discuss this in more detail as soon as the first beta is out...
Lukas.