gacharmin,

having a paper ticket won't have helped you with NW since other passengers are holding e-tickets. Besides, NW probably couldn't even forward the flight plan to the pilots.

my experience with e-tickets in general:
never had a problem domestically or internationally involving one-carrier travel (ie. no interline baggage transfers).

The only incident so far was at LHR. UA at LHR, not Paddington, will not even let you approach the check-in counter without a receipt. That's was a pain.