I access isolated networks/labs via SSH SOCKS proxies. This plugin lets me access a particular lab simply by right-clicking on the new tab button and selecting the lab/network that I want to browse in. I wish there was an option or shortcut key (similar to Ctrl+T or Ctrl+Shift+T) to open a new tab in the same container as the current one, but this is still a huge win.

I've experimented with using it to isolate my personal browsing while on my work computer and while I don't know if my cookies are being separated, I'm pretty sure my browsing history is not. Oh well, it's still great for the first use case! :)