The scope of My First Conference was huge. We took over the city's convention center and the neighboring hotel. My father didn't believe me when I said there were 10,000 people there. And it's true that I exaggerated. The official program guide declares that attendance is only "approaching 8,000". This includes 14 poster sessions of 232 posters each (that's 3,250 posters, each with at least one accompanying author). There were 42 different possible events to attend in the first session of the first day, each with 5 speakers (another 2,950). And then there's all the people who came despite not giving any presentations.
The good news is that the 8,000 people were nicely spread out, and the only time I felt the presence of the crowd was when waiting in line for coffee or trying to find a place to sit in coffee shops or restaurants. The bad news is that it was an almost completely anonymous conference; there was no chance to meet or even recognize other people interested in the same topics. I barely managed to find the people in my lab; fortunately, we were mostly attending the same sessions.
That said, I was recognized by someone from my undergrad university. I have no idea how she managed to recognize me, given that when I was in college my hair was two inches long and spiky (and, for one year, neon blue), and now it's shoulder length. I didn't recognize her at all, so perhaps the conference isn't so anonymous for anyone with a decent memory for faces. But the size still has to take some responsibility.