I went to one in jeans and a button up shirt. It was half people straight from work dressed very well and the other half ranging from business casual to a current student in a t-shirt, jeans, with flipflops on. The student events are a lot more relaxed so wear whatever you want. Students wont hold it against you if you are wearing a poloshirt.
I didn't take notes since I was looking more at what the people were like, their impressions of the school, and just overall fit. I didn't want to take away from things just to take notes.
I didn't get business cards though the one female current student was making a point to hand them out to the other females there...she pretty much aimed at talking to the other females.
Like I said I went to the event more to gauge the people and their views of the school not to get lots of inside info. I am planning a school/class visit so I think thats where I will pick up some details for my essays. This was more of to see if I could see myself attending the school. It was actually a far better experience than anything with adcoms, since people weren't trying to put on a show. I learned a lot about the school, the people, and the city...much more than I had thought I would.