mp3split is an awesome command line utility to split long audio files using silence detection.
It takes some playing around with to get used to all the options, but it is extremely powerful.
The defaults work great in most cases and you can simply cat files back together if it splits them too much. I discovered mp3split after downloading a live Nellie McKay concert from NPR. see my blog post here Nellie McKay The concert is a single mp3 and I wanted to split it up so I could skip tracks when listening to it on cd. To use all the defaults the command would look like this.

mp3splt -d Nellie_McKay_ASC-Live -s -f Nellie_McKay_ASC-Live.mp3

where -d is the directory you want the ouput files to goto and -f is the file to split
I ended up using something more like this after reading the man pages.

mp3splt -d Nellie_McKay_ASC-Live -o Nellie+McKay+ASC-Live+@n -s -a -p min=2 -f Nellie_McKay_ASC-Live.mp3

It worked great. Dont't use just love needing something, downloading it for free and having it just work?
apt-cache search mp3 | less
// split
sudo apt-get install mp3splt
man mp3splt