Because I do not use Xubuntu, I can't spot the exact changes between Xubuntu 10.04 and Xubuntu 10.10, but I'll try to post an overview of Xubuntu 10.10 beta anyway. For reference, here is how Xubuntu 10.04 Lucid Lynx used to look.
Xubuntu 10.10 Maverick Meerkat, the XFCE Ubuntu flavor got a lot of changes since 10.04, starting with a new default wallpaper and theme:
The theme looks amazing, don't you think? The GTK+ theme is based on Zuki Blues and the Xfwm theme on axiom. The icons, just like in Xubuntu 10.04 are Elementary Xubuntu.
I believe this is the only Ubuntu flavor that comes with a branded wallpaper. But who knows, maybe Xubuntu will also get a new wallpaper until 10.10 final is released, even though the UI freeze has passed (like it will happen for Ubuntu 10.10).
There are also some new applications in Xubuntu 10.10 beta! Totem has been replaced with Parole Media player and Brasero with Xfburn:
The other default applications remain unchanged: GIMP Image Editor, Exaile, Firefox, Pidgin, Thunderbird, Abiword, Ubuntu Software Center, and so on. You know, all the cool applications which are missing from the default Ubuntu installation. And of course, Xubuntu also comes with a clipboard manager installed by default - Clipman:
Changes have also been made to the way the login screen looks like:
And to the shutdown dialog: