My flatmate's boyfriend is fond of throwing large house parties with hundreds of invitees, then hiring a doorman to check names off against the FB RSVP list. If you're not on it, you're not admitted.
My closest friends remember me and send me invites via email, but I can't fault them for forgetting now and then.
I'm very close to my wife and can't imagine getting a divorce, but I think it's healthy that we manage our own social calendars.
In short: pointing to the line between friends and "friends" and (likely my personality coloring the value judgment) thus questioning whether you're actually missing out by not being so closely connected to those "friends".
(Frankly the very concept of a house party with so many attendees that don't actually know one another, that a door man and a guest list is required, sounds like a caricature of a straw man I might have cooked up to have a laugh at "things you might need FB to get invited to". But maybe that's just saying more about me and why I don't grok or value things like FB.)
It's definitely naive to think "oh, if you're really friends with them you'll remember their name without the help of a computer." This is especially the case with larger more inclusive weddings where now-disconnected friends are invited.
That said, I find it challenging to remember my immediate families birthdays (not to mention, anniversaries etc) and while my crutch has always been a calendar, FB can provide that crutch for folks who don't have a calendar habit.
Bottom line is that the core premise of FB is actually quite sound, its just not easily monetizable. Its possible that after a while folks would pay to subscribe to a FB like service but long before that Google or someone else who isn't being held against the wall with a share certificate pointed at their head may find a more workable solution.
And of course FB could, their are a lot of smart folks over there.
Also, birthdays? Aren't those the sorts of things you find out about once per friend and then add to your own contacts? I've never had a Facebook account, but that's not a problem I've ever experienced.
Granted, I don't automatically know the birthday of every single person I meet or even get a number/email from. But I would go so far as to call that a feature, and because of that, the birthday notifications I do get are worth getting.