Depends on the crowd and the day. Some days I don't notice anyone unless they're really loud or in my way. Other days I'm hyper aware of everyone around me and I'm the one initiating the 'did you notice' conversation.
At restaurants I tend to always end up having my ears fucked by really disturbing or ignorant conversations in booths around me though. I wish I could tune that out.
In really crowded situations, I try to aggressively filter people out of my perception as much as possible. Mostly because if I'm really AWARE of all those people that damn close, I want to start lashing out with knees and elbows until they clear some space.
I'm a lot more likely to look at / notice random people in situations like restaurants, because you have defined territories - this is my table, this is their table, et cetera. People for the most part at least try to respect those boundaries, which leaves me feeling more relaxed.