NEW VERSION! http://darkimmortal.com/2012/08/darkelec-release-2/

None of the currently available solutions do a perfect job with running XBMC on the Pi, however OpenELEC comes by far the closest, in spite of its locked down nature.

This fork aims to remedy the very few flaws in its implementation and to focus 100% on the Pi, while also sticking to the upstream and incorporating its updates.

Features:

Low idle CPU usage (< 15%)

Smoother and more responsive

Built in XBMC addons: iPlayer, custom fixed version of Demand 5, various unofficial repos

iPlayer, 4oD, Demand 5, ITV Player, SportsDevil all fully tested+working

Improved wifi connectivity

Added test-connman scripts for easy wifi setup (see here)

Added wireless_tools (iwconfig etc.)

Added rndis_wlan wifi driver (broadcom 4320 chipset)

Easy SD card installation script for building from source ( ./install [block device] )

Download pre-built SD Card image: darkelec1.zip (~75MB)

(Fixed partition size at just under 2GB total, you can expand manually with GParted if necessary)

Source: https://github.com/darkimmortal/DarkELEC

(Refer to Building and Installing OpenELEC for Raspberry Pi – expect build issues on anything but a stock debian squeeze i686 install)