Crappy actions: You have offer. People from the firm email you to say congrats. No one hears back from you. What is so friggin hard? Hit reply and say "thank you, I enjoyed meeting you during my visit and will definitely get in touch if I have further questions." (This assumes you are still considering firm). We don't understand when people go silent.
Dumb action: You are still interested in firm but we haven't heard from you in weeks. Yes, you are probably on hold, but if you like us why not let us know you are still interested. Candidate A got an offer a couple of weeks ago because candidate B had gone silent and we figured not interested.
Crappy actions: You accept offer, or after you get offer, firm sends you a goody basket of treats, firm toys, whatever. Drop an email and thank the hiring coordinator, the HP, someone. I realize I sound like your mom telling you to send a thank you note to grandma for the bday gift, but these are common courtesies that seem to be missing. Same goes for stuff sent to you when you pass bar, graduate law school, etc. Acknowledge and express appreciation.