After my first upgrade to Karmic Koala, virtual box stopped working. After several attempts, went back to Jaunty. Several days later, upgraded to Karmic. Virtual box worked fine, but Skype stopped working. Tried several things including re-installation of pulse audio. Nothing worked. After a few days tried Skype, it was working. Can't explain why it started working all of a sudden.

Just saw a video of Ubuntu Karmic on BBC technology site.The title.
Ubuntu readies the Karmic Koala
This is the link.

http://news.bbc.co.uk/1/hi/technology/8326264.stm?ls
Ubuntu's Chris Kenyon gives BBC Radio 5-Live's Gary Parkinson a preview of Karmic Koala.
I thought it was great! P{erhaps I am biased because I have been using Ubuntu for a few years now.
Bhupendra

Eversince upgrading to Jaunty my sony walkman 8gb mp3/4 player was mounting but was refusing to show any of my music folders. An extensive search on google did not solve the problem.
Then I enabled usb/sony walkman in the virtual box; I have installed Linux Mint (as a demonstration to win over a friend to Linux distros) The Walkman mounted and showed all my music folders. When I disabled the walkman in the virtual box, lo and behold!, it showed up as a usb storage device on the Jaunty...

Eversince upgrading to Jaunty my sony walkman 8gb mp3/4 player was mounting but was refusing to show any of my music folders. An extensive search on google did not solve the problem.

The upgrade to Ubuntu Jaunty Jackalope went smoothly. It has not crashed since the upgrade. It looks great and is fast.