In XFCE when I put the mouse over the workspace switcher in the taskbar and roll the middle mouse button, it switches the workspaces.
When I do this in a Gnome session, nothing happens.
So now what?
Mouse scroll workspace switch is Xfce4 feature. User can enable or disable switching by placing mouse over Workspace Switcher, right click-Properties. Feature can be very annoying if you do few things at a time in different workspaces. If I remember correctly, Gnome2 has same option.