The 4Gb versions (minis) seem to freeze more than the regular ones. You need to reset the iPod in order to get it functioning again. To reset:
Hold the menu and action (middle button) together.
This should reset the iPod.
I have heard some people mention that occasionally some albums appear to be missing after the reset due to database corruption. I have not witnessed any db corruption on mine so I cannot speak to that issue.
The 4Gb versions (minis) seem to freeze more than the regular ones. You need to reset the iPod in order to get it functioning again. To reset: