well, i never did relay back my experience with the english MUI setup, but i was able to successfully install it. actually, at first, darkside6 didn't work for me immediately after installing the cab. rather, what i had to do (as one post in the previous thread tipped me off) was to find the extracted individual cabs in the temporary files folder and install them separately. after that and a soft reset, things seemed to be installed fine. most menus were changed to english (with the exception of the menus in the Softbank mail program and some drop-down menus, and shortcuts in settings).
one thing i wasn't sure about though- well, actually two. first, for the clock. i changed it so it shows a 12 hour clock instead of a 24 hour clock... but there is no AM or PM following the time? is that how it displays on native english roms? second, i've heard some people say that to get rid of the english menus and revert back to japanese, you have to do a hard reset. does this mean that it's safe to uninstall the programs listed in the installed programs list related to the MUI? i'm not a fan of hardresetting, and would like to avoid screwing up my quite functional setup if it's not necessary. but if its just taking up unnecessary space...