The Facebook approach is nice. The number they show initially varies with screen resolution and their scrolling and lazy loading work well.
Most of it would be relatively easy to copy, although I suspect a lot of testing (or a lot of bug reports) have gone into correctly guessing the number of elements to show based on screen size.
The best thing imho about their approach is that they react to all page visits, and very clearly show a bold notification for a notification sent after you visited that page and a more subtle version for a notification that you have already seen the triggering change for.
That's how they solve the feeling of being overwhelmed by notifications. It keeps the new number down and means that a new notification should only refer to a change you have not seen.
Sadly most people (including us) compromise and show notifications as "new" if you have not seen the notification before, and clear their new status before you click through rather than maintaining the relationship between trigger and notification to give a more accurate version of "new".
The Quora compromise on the same UI feature is different but silly. They keep notifications marked new until you manually clear them. I rarely use Quora and have a completely useless readout that tells me I have 200 new notifications.
Unfortunately I think adding "untriggers" alongside all the notification triggers is significant work, so it should remain a potential future enhancement.
Luke Welling