I found a little piece of software, called Contacts Scrubberxxx8482; for Outlook®" (sorry if i don't submit the link, but i can't , only three posts don't allow it), it manages all your duplicated contacts in Outlook and rearrange your contact' profile in a few minutes.
What i did to have a clea address book in my BB:
1) i made a backup of bb databases (backups avoid probems anyway!)
2) i've cleared my 2 bb address books (still don't know why two, however...)
3) i did a "scrub" of my Outlook 2003 contacts with the software described above
4) then, reconnected the device to the PC opened DM and i've synch from Outlook to BB address book
Done! no more multiple restaurants or pals
I hope sincerely it's not just an illusion (i'm writing and now it's 5.00 am!), but it seems it really works