I think it would be the separation between "real life" and "online life".

Getting hacked used to mean either restoring a page from a backup, asking your friends to help you get some gear back, or deleting posts on a forum.

Today, getting hacked leads to empty bank accounts, identity theft, and real life fallout.

I miss the anonymity that was the "default", when the logged in user was the data product, not the person behind that user.

Most of all, I miss the community that used to exist with their odd etiquettes and diverse ideals. It was a delight to stumble across new forums, now it always just seems to be more of the same.