What's the etiquette for a short visit to a US university department by a faculty member from another university? In May, I'll be visiting a department at Columbia University in the US for a few days. What's the etiquette on visiting (answers relevant to US in general are welcome, to prevent this question getting too localised)?

I'd like to spend some time with quite a few of the researchers, and compare notes on ongoing work. I'll read their recent publications in advance. Should I be inviting staff out for a coffee and a chat; or dinner; or a talk in the lab?

Context: I'm a faculty researcher, and would be looking to spend a bit of time with postdoc researchers, and those professors whose jobs are primarily research, rather than admin or teaching.
I think you are the person who would be invited out to lunch, dinner etc. as you are the guest :) ! However, there is nothing wrong with inviting your opposite number to talk in an informal setting. The only consideration is that you know the lay of the land! 

Depending on how many days you would be spending at the US university, you might want to make a strategy on conversations and prospective collaborations. 

I am assuming you would have results to show and tell and with a punchline at that. That generally helps.