I’ve been using Firefox 3 for about a month now, using the same method Lifehacker explains in this article, with Portable Firefox 3.  This allows you to keep your normal Firefox 2 install and not have to install Firefox 3 until it comes out of beta.

BTW, Firefox 3 is absolutely amazing.  The speed is incredible, especially with the javascript heavy web applications I always use, like Gmail, Google Reader, and Remember the Milk.

And second BTW, PortableApps is amazing also.  It keeps me from having to install the plethora of open source applications I use periodically, leaving me with a slender hard drive with fewer applications installed.