I have started to use Mozilla Webrunner on my Mac: used in conjunction with Quicksilver, this is a neat way to start web sites as standalone sand-boxed applications. This does not replace tab browsing, of course, but is very useful for the applications you usually dock on your second monitor (or third one, if you are a real guru), like your continuous integration server dashboard or your web mail home page.
To have Quicksilver bootstrap Webrunner applications, simply store your profiles in a directory that you register as a custom catalog. And voila, you can launch your web applications with a few key strokes.
This is another way to reduce the latency between thinking about what the computer should do for you and have it actually do it. When you think at the zillions of cycles the computer wastes waiting for you, any tool, gadget or utility that helps minimizing this loss is to be lauded!