Pinned tabs are really nice.  I have one for email and one for calendar and they're always exactly where I want them.

Sometimes, however, I click on a bookmark without holding ctrl- and it replaces the contents of my pinned tab.  This isn't a big deal for me: I hit the back button and then ctrl-click on my bookmark.

I've noticed, however, that my wife gets hopelessly lost when this happens.  She ends up with pinned tabs that she can't close and don't have what she wants them to have.  She ends up opening a new tab so she can get to a page with the "Google apps" grid from which she can open her email.

I suggest that bookmarks NEVER open in a pinned tab and instead always open a new tab if a pinned tab was active at the time.

Another option would be a setting such that bookmarks always open in a new tab.  It's rare that I want to replace an existing tab anyway.