Though I haven’t used (and won’t use) Ubuntu, it has a few things I appreciate (as far as I know them):
Ubuntu One: I wish we could have something similar for Debian users (ideally, it should be extended so that we could sync our calendars, contacts, liferea data etc.).
usb-creator: seems the easiest way to create a [...]

Though I only use Debian on all my machines, I like playing with new Ubuntu releases, just in case I have to set it up on someone else’s machine. I use VirtualBox for testing.
When trying the upcoming new Ubuntu 8.10 release, and after installing the VirtualBox clients on the guest, I had the following issues: