Ubuntu's next version will feature Unity with Compiz as the window manager
if you have compositing (3D graphics). If not, then it will install Unity
2D. The original plan was to install GNOME 2.x which is what it has now, but
they unveiled Unity 2D a weeek or two ago. It caught everybody off guard
because most people did not know they were working on it.

Unity 2D or full Unity will feature one universal taskbar at the top and a
panel on the left side with icons. The taskbar will change to reflect the
application that you are using. Both the panel and the universal taskbar are
copying Mac OS/X. They are moving away from the idea of virtual desktops
(the boxes that allow you to switch to a new desktop on the bottom panel in
GNOME) and into the idea of workspaces. This is the new thing in Unity and
GNOME Shell. It changes the way we work and many people will find it
frustrating in the initial stages.

You can still install GNOME 2.x for the time being, but eventually the
project will die as GNOME have moved on to other things. You can also
install GNOME Shell (what they have moved on to) which is due out in the
Spring. GNOME Shell is similar to Unity. It has a universal taskbar at the
top, workspaces and a side panel, however it works differently and looks
very different. Both GNOME Shell and Unity will take some adjustment on the
part of the user.

What you have to give up using in either is the Compix cube and a bottom
dock like AWN, Cairo or Docky. You can use them, but it does not intergrate
well into GNOME Shell or Unity and can confuse you even more. If you use a
bottom dock then it takes away from idea behind the side panel and if you
use Compiz cube it adds virtual desktops to workspaces effectively creating
a confusing situation. Also GTK apps should work well with the universal
task bar but KDE apps and others that are neither such as Chromium will not
support it, so you will have the old application panel that you get now plus
the useless Unity or GNOME Shell universal taskbar. All of this adds
confusion when ypu are trying to learn a new interface. Maybe once you
adjust you can find ways to integrate them.

I have used both and still prefer KDE. It has been through the change over
and I like the way it works. I have heard that Mint will stick with GNOME
2.x and wait on Unity. Smart of them. Users who do not want to try Unity can
stick with 10.04 until April, 2013 and 10.10 until April, 2012. I suspect
quite a few people will take a wait and see approach.