MOC is available on the repositories in Raspbian (2.5.0-alpha4 release). Recently an high CPU usage has been signaled by using ‘mocp’ player on RaspberryPi (http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=24647&p=257780).
This bad behavior is currently undergoing review, in the meantime those who uses MOC can run the following command to bypass this problem and reduce (very) the CPU usage:
$ mocp -O "ALSADevice=hw:0,0"
It should use the ALSA hardware directly without the software layer in between format conversion and resampling.
Update (January,23 2013): according to the MOC forum, this issue is tied with a bug in ALSA, probably the one fixed in alsa-lib commit 3fd4ab9b, and is sensitive to sampling rate and sample width.
Version 1.0.26 on Fedora does not exhibit this bug on the RPi.
(Here the MOC rpm for Fedora 17 ARM).