100.0% usage by Audio codec hwC0D0: Realtek

I ran powertop, and it says that the Realtek audio codec is using 100.0% of the cpu. Is this a problem?

I'm running Ubuntu 11.10 32-bit on Intel® Core™ i7 CPU M 640 @ 2.80GHz × 4 Sony VAIO laptop.

Try changing "Enable Audio codec power management" to good in the Tunables tab for powertop. After doing so, hwC0D0 is no longer listed in powertop for me.

No, it just means that you have (probably digital) sound output enabled. If you have some sound outputs, such as digital (optical/coaxial) or hdmi you are not using, then you can blacklist their drivers and you might save some battery. They will be listed in lsmod something like, snd_hda_code_realtek and snd_hda_codec_hdmi. By adding these to /etc/modprobe.d/blacklist.conf you can disable them.

I found that muting the microphone input in the mixer solved the problem. I use a Dell XPS17.