There was apparently a big privacy bug where when you posted status updates, even people who shouldn't be able to see your updates would be able to see them. I think there were issues reported with birthdays too, and such, but that was the big issue I think as far as 3.0.1.
So how did this update get pushed so fast when 3.0 took 12 days to get accepted? Yes this is just an update but 3.0 was an update to 2.5 technically. I can see if because of the whole privacy issue it got released quicker and I'm certainly not complaining but I wonder how this got pushed and accepted so quickly compared to 3.0.
Also fyi for those that had it, the notifications error was a server-side issue that got fixed earlier today.