This topic has certainly spawned an active discussion! I have no idea what my life list total is, but I'd guess it's closing in on 1000. The majority of those would be from outside North America. I completely agree with several others that not all lifers are created equal. Some are burned permanently in my memory, but many more are totally forgotten. Much depends on the circumstances, the bird, the location, and even who you were with.
25 years ago, I was a dedicated lister. I documented every birding excursion and could tell anyone willing to listen, exactly what my year and life list totals were at any time. There were several factors that made me stop. One was the time required to manually record it all, but another was the realization that I was becoming a slave to the list. I would go places that had the best listing potential rather than ones that might actually be more interesting or provide great viewing opportunities for only a few species. The thing that really "cured" me from listing was travel: enjoy the moment and don't worry that you just missed 5 lifers that you may never have the opportunity to see again!
Lately, I have fallen off the "non-lister" wagon and started using eBird. I still don't fret about the numbers, but it seems like a worthwhile exercise when the observations become part of a public database instead of sitting in a filing cabinet. I think the database is important. I've seen significant changes in bird populations in the time I've been birding. I see the value of a database, rather than just my feeble memory for tracking those things.
BB