As you may know, I've been on a little odyssey to make pipelining safe, fast, and aggressive. I've got a dozen patches for Firefox 4 that do that.
This post is your chance to try them out. Download a build for your favorite OS and try them:
You will still need to set network.http.pipelining to true in about:config in order to enable the code. You can also set network.http.pipelining.aggressive to true if you want to disable any of the "gently test the waters" code. I do that when I want to measure the pipelines, but leaving aggressive mode off is probably a good idea if you want to ensure the smoothest experience possible, but I gotta say that the various recovery mechanisms are working well enough (and are used rarely enough) that I am considering making normal mode considerably more like aggressive mode.
Consider this a beta level pre-test. I want your feedback and any bug reports.