Whats the difference from eg 1.8.2 to 1.9.1

Im still on the very great and cool spip v 1.8b2
And Im happy.
So is there anywhere I can see what "benefits" I would get out of  
upgrading..
and if not, do you guys have a few words on the benefits eg, new code  
etc.. that I would get out of upgrading..
kindly
Tom