Since you can now 'tap', 'rap', and 'bang' on doors, I also added 'buzz' to apartment doors. This is more than just a fancy knock.
If you're the renter, offline and sleeping on the other side of your front door, when you're buzzed a quick little message will be sent to your email, informing you that someone was looking to roleplay with your character.
Additionally, the 'examine' for apartment doors is much more useful.