You could uncheck the boxes, but by default they were all checked and everything started syncing the moment you signed in.

I remember because it bothered me to have to wipe my passwords from some random pc I was using just because I wanted my bookmarks.

Nope, clicking "Turn Off" under sync says:

> This will sign you out of your Google accounts.

And sure enough, it signs you out of gmail and the browser. So it's sign in to the browser, or no gmail for you.