I often have the need to quickly test something in a different browser, so I have a few installed on my Windows 7 laptop, and others (often older versions) running in VM’s. Obviously this works OK but can be a pain to boot/resume a VM for a quick browser test.
I happened across this today which works quite well: http://www.spoon.net/browsers/
This installs a plugin that runs the browser from the web.
I guess it’s directly analogous to Microsoft App-V, VMWare ThinApp and Citrix XenApp virtualisation.
Except this doesn’t need a massive infrastructure to run!