It's on a letter by letter basis though, maybe best to only update the browser hash say after a second or more of no letters added to the search bar.

Upvote.

What I've done for now is only updated the history/hashtag when hitting enter, similar to Google Instant. They have some other conditions in there as well, but there's not a whole lot of a use-case on here for wanting to use the back button within a search query.