I've [only] been to three tech conferences. The only "sexism" I observed was excessive delight: "Oh wow, a woman!" which I hardly consider harassing. No one meant disrespect; rather the opposite. Possibly offensive is the notion that it would be a surprise to find me there at all. I might say something similar to a man at a needlepoint conference.
Yes, I got sexual attention, but only in a social context, and nothing inappropriate. I've also gotten "Let's be friends!" attention from people, including other women. In other words, we are there to meet people who share our interests, on a social as well as professional level.