Yes, history, bookmarks and extensions are separate. I have one profile for "me in my personal life" and "me at work", and a few for testing logins to different interfaces at work. So this degree of separation is mostly what I want, although it can be a little annoying to maintain the extensions you want under both profiles.

Keeping history separate in particular is very valuable since nowadays the fastest / least hassle way to bring up a site is to start typing the beginning of the URL in the navigation bar, so you wouldn't want work URLs mixed in with non-work URLs.