my experience is

1. Lounge access: ^
2. Lounge quality:^ some lounges are ok, some good, some are nothing special. they should try to have "good" as a standard
3. Priority check-in and lists: ^^^
4. Telecheckin: t^ sometimes it works sometimes it doesn't depending on the destination
5. Luggage: ^
6. Priority security: ^^^
7. Priority in boarding: they never ever enforce the lines! damn
8. Elite phone line: ^^^
9. Elite email handling: never tried
10. Upgrade certificates: tried to book a mxp-jfk but there's never availability in Y- B- M class