There exists a wikipedia formatted to mobi. However the newest version (from 2008 I think) splits up into several files and has an index file (or more index files) that redirects from each keyword to another file.
However the hyperlinks from one document to another work well for mobireader, but aren't even recognized by my kindle 2. (I don't know if that's generally impossible with the kindle, or just doesn't work with the file.
however the files can be found here:
http://pinguinburg.de/wpmp
I think there is explained how to use any html dump to convert to mobi.
I use a pretty old german wikipedia that still comes as a single file (about 300 MB or something like that) and has been converted to mobipocket.
it can be found here (only german):
http://www.axelschaefermdb.de/servic...ia/archiv.html
http://de.wikipedia.org/wiki/Wikipedia:Unterwegs