Hell!, sometimes when it comes to playing audio/video, advanced players like MPlayer can actually play your content with the same amount of quality still using less system resources when comparing some of the "paid" multimedia players for Microsoft Windows for instance.
Anyway, let me get back to the story, if you want to convert between a lot of different audio files in GNU/Linux then you should consider Gnac!. I do criticize Gnome's idea of simplicity whenever it's been reminded ;-) but even though Grac also has a simplified GUI which is written GTK+, yet it comes with almost all the features that one needs in an audio converter without a doubt.
The developers recently released a (May 5th, 2011 actually) new version which now add the support for extracting audio files within the video container itself as well.
*. Since it uses the Gstreamer, it can convert between all the major audio files with ease - mp3, aac, wma, wav, ogg, etc.
*. Edit track/year/album-name/artist name from the app itself.
*. Change bit-rate and sampling rate, etc.
*. Change the storing location of the converted audios.
*. Add album-art/covers... are few of the main features to mention.
You can easily install Gnac in Ubuntu 11.04 Natty Narwhal (should work on 10.10 and 10.04) by entering the below command.
sudo add-apt-repository ppa:gnac-team/ppa
sudo apt-get update
sudo apt-get install gnac