Frog Design posted a piece called Making Sense of Occupy, extolling the virtues of well-aimed photographs to avoid stereotypes and to tell a complete story.
I'd extend the observation about the value of photographs to include the value of primary recording of any kind, including audio. A first impression of something vs. what can be seen or heard in a later moment away from the event can be night and day.
Once when I interviewed a woman I thought to myself that she had nothing significant to say. Listening later to the recording, it was like a ghost in the room was saying stunning things - how could I have missed this on first hearing? Well, the act of seeking can be a distraction from taking it in.
Researchers and designers under great time pressures push for immediate discoveries from observations. All the more reason to "cover" an event. Yes, discover onsite. Focus on the hypotheses at hand and the unique behaviors being expressed. But also remember to pull back, allowing for the possibility of discovering points later. In the processing ("groking") is where many significant discoveries and new research questions pop up.
Moral: Don't rely on notes or your memory. Don't rely on your own socio-cultural categories or those of others. Get it on camera or on audio. Practice "covering" the parts and the contexts.
Experience researcher in high tech and built environments with an anthropology provenance.