the stock wipe in OR do not touch the ext partition of the sdcard...
in Minimod OR i add a script to wipe the ext partition as well
you can do a nandroid of your ext partition bevor (its just a tar file, that you can unzip on your pc) and after updating you can try to restore it...
also a plroblem by using a ext partition is, when the dalvik-cache also is moved to the ext, you cant wipe it over OR, you must do it by your self using the console ( rm -f /sddata/dalvik-cache/* )
also a solution if you have problems with updating to cm7, open the cm7 update zip and delete some apps/media files to shrink the size of the file, on some devices some blocks of the flashrom are broken and then the update fails (fore me it help, cause i had some problems bei trying it first)
i hope i can help someone
and sorry for my very bad english ^^