|Update Manager performing the upgrade|
|Firefox 4.0 in Natty; update Natty and you should get Firefox 6.0|
Unity also makes its debut as the default desktop experience on Natty for hardware that can handle the 3D effects. It's still rough though since it initially appeared only on the netbook edition of Ubuntu and the developers rushed it out for Natty. 6 months just isn't enough for a desktop to mature properly. Let's hope for a much improved experience in Oneiric.
LibreOffice and Banshee take over as the default installed office suite and music player respectively. Due to there being way too much change happening at once, we didn't get to see a transition to Gnome 3 in Natty but that's already happening in Oneiric.
That's up next - upgrading to Oneiric (development release)