You've definitely had this shift from chinos/button-down shirts/boat shoes business casual (i.e. more or less traditional East Coast preppy) to jeans/hoodies/t-shirts/sneakers among much of the tech set at least outside of settings like meeting with customers.

I used to pretty much always wear the business casual "uniform" but a few years ago I found myself going a bit more casual at the more developer-oriented events I would attend because I was starting to feel overdressed.