Worth a try? Yes.

Better Tab handling and has the ability to hold tabs in "groups" and a "panorama" view which allows you to view all tabs across groups.

The awesome bar has also improved significantly and has some smart features (like the option of tab switching instead of opening a new tab when you already have a URL open).

Better Add-ons management interface and some add-ons work without a restart of the browser.

Websockets disabled (for security)

I still prefer Chrome though.

PS. I've been using the FF 4 beta version for a 3-4 months now and probably dont remember the other significant changes.