(I write this because I have talked quite a few times about the subject but never offered any use cases for it.)

We have a core group of Gentoo Prefix users in #gentoo-prefix on freenode. I took a poll and gathered up all the use cases for Gentoo Prefix. They are in somewhat of an order:

• Bringing a Gentoo userland to your MacBook (macos/darwin) – without modifying the eye-candy host OS.
• Allowing easy package management on your host where you do not have privileged access.  No more manual ./configure --prefix=~/foo && make && make install
• GNU-ifying your non-GNU host, like Solaris, HP-UX, AIX, etc. (userland only, of course)
• Providing a similar environment across distros for your simulated build/customer environment.
• Using the familiar Gentoo/Portage on a non familiar OS
• “I use Gentoo Prefix because it is cool” -grobian

For a more detailed use-case analysis on some of the points above, please [read here][3]. Otherwise, enjoy!

[3]: http://www.gentoo.org/proj/en/gentoo-alt/prefix/usecases.xml