I've never understood how DRM can be stripped from a mobi file. I've never been able to find the files when I looked on my ipod. (I think I've shown my lack of hacking on the ipod with this comment--eep!).
Usually you use a general computer to strip the DRM. On a Mac or PC you have a program masquerade as a client (like Kindle for PC) and then remove the DRM from the contents it get. MyTunes was for Itunes was like that in the past.
