From what I hear, the answers are yes and yes.
I haven't upgraded yet (lazy), but the consensus on the entourageedge.com forum seems to be that the Ermine upgrade improves speed and adds functionality. Some people have experienced problems -- browser crashes, problems waking from hibernation (more on EE than PE), green camera pictures -- but most people who have had to downgrade to fix something have upgraded again. You can read all about it in the Ermine forum at
http://www.entourageedge.com/forums/forum.php.