I find the Unity desktop that ships with Ubuntu is clumsy to use over VNC. When changing workspaces, for example, it shows a full screen overview of what is on each desktop, which takes a long time to load over a slower connection. I'm sure it is very beautiful when sitting in front of the machine, but it is grating when used over a remote connection.
Also, there seem to be some exotic keystrokes (e.g., ctrl+alt+arrow to switch workspaces), or lots of middle and right button work on the taskbar, which often don't translate properly down a VNC.
To switch desktops, first install gnome with
apt-get install gnome-session-fallback
Then, to configure VNC to launch into this, change the file .vnc/xstartup so that it has the line:
exec gnome-session --session=gnome-classic