Raspberry Pi Quick Install Guide
Installing Gentoo onto a Raspberry Pi is relatively straight forward and in some ways easier because a kernel image is provided by the Raspberry Pi Foundation. This means you can get Gentoo installed quickly onto you Raspberry Pi.
Preparing the SD Card
The Raspberry Pi boots off a FAT32 /boot partition, you will also require a root and swap partition.
Create the Partitions
Use the fdisk command to create the partitions.
Create the File Systems
Installing onto the SD card
Mounting the partitions
Extract Stage 3 Image
Install kernel and modules
The Raspberry Pi Foundation maintain a branch of the Linux kernel that will run on the Raspberry Pi, including a compiled version which we use here.
Configure the system
Edit the fstab to match your partition scheme.
Set boot options
You need to create a file cmdline.txt in /boot to pass options to the kernel.
The default make.conf includes basic CFLAGS. If you would like to change the settings to something more 'optimal' for the Pi look at the details on the relevant wiki page.
Configure time zone
Find your time zone using this command.
(Suppose you want to use Europe/London)
(Next set the timezone)
Clear root password
As we do not chroot before we boot, you will need to unset the root password. Allowing you to login with a blank password for the root user.
Edit the line for root so it looks like the example below.
Unmount SD and then boot your Raspberry Pi
Unmount the SD card.
Plugin the SD card to your Raspberry Pi, make sure you have a keyboard and monitor also plugged in then connect the power. Hopefully Gentoo will boot giving you a login prompt, login as root and no password. During the first boot you will see a few warnings and errors which we will fix in the next section.
Post boot configuration
Set root password
Immediately set a root password.
Enabling networking on boot
Assuming you are using DHCP on the eth0.
List the available profiles.
Select the desired profile, for example  default/linux/arm/13.0/armv6j:
Configuring inittab and rc.conf
Uncomment the linux specific rc.conf rc_sys value, to stop warning in boot up.
Comment out the s0 Serial console to stop "INIT: Id "s0" respawning too fast" messages on the console.
Enable software clock
The Raspberry Pi does not have a hardware clock, so you need to disable the hwclock daemon and enable swclock.
If the date/time displayed is wrong, update it using the date MMDDhhmmYYYY syntax (Month, Day, hour, minute and Year). At this stage, you should start use the timezone you setted before in the Configure time zone section. For instance, to set the date to May 02th, 04:21 in the year 2013:
Enable SSH Daemon
It is very easy to overclock a Raspberry Pi up to 1000MHz without affecting your warranty 
To enable overclocking select one of the suggest modes from the list above, "Medium" is generally a good starting point. Edit the /boot/config.txt, add the appropriate values and reboot the Raspberry Pi for changes to take effect.
To manage the CPU frequency scaling you can use the cpufrequtils.
The default scaling governor can be changed in the /etc/conf.d/cpufrequtils file
Confirm the current scaling and CPU using the cpufreq-info command
Force Turbo Option
The force turbo option turns off the dynamic clocks and runs the Raspberry Pi constantly at the highest arm_freq.  Edit the /boot/config.txt, add force_turbo=1 then reboot the Raspberry Pi for changes to take effect.
Changing memory split
Not strictly speaking speaking overclocking, but the memory used by the GPU can be changed. To change the memory used by the GPU down to a minimum of 16MB add the gpu_mem value to /boot/config.txt, then reboot the Raspberry Pi for changes to take effect.
Cross building (Optional)
This is not strictly required, but it is extremely practical given the source driven nature of Gentoo. Building almost anything on the Raspberry Pi takes a very, very long time - especially when there are a lot of dependencies involved.
Fortunately, you can offload much of the heavy lifting work to a more powerful system (such as your main gentoo desktop/server) using crossdev and distcc (though this will only work for packages must compile c/c++).
Full details of using distcc and crossdev on the Raspberry Pi are described in Raspberry Pi Cross building.
Install Video Core Userland tools and libraries
The ARM side libraries for interfacing to Raspberry Pi GPU are included in a package raspberrypi-userland. Which includes the Video Core tools, GLES2, EGL, openmax and openVG libs that support the Raspberry Pi GPU.