A few days ago I installed Ubuntu 12.10 on a 2009 laptop (a Dell Latitude D820). This laptop has a trackpoint (the little nib between the G, B and H keys on the keyboard that functions as a mouse). The trackpoint has its own set of mouse buttons, but, unlike my present Thinkpad, it doesn’t have a middle mouse button.
From my early Linux years I remembered that you could use a simultaneous click on the left and right buttons of a mouse to emulate the click of a middle mouse button. This option had to be set in the Xorg configuration file. My guess was that by now this was no longer needed, but I couldn’t find the appropriate option anywhere in Ubuntu’s settings. It’s quite a shame to see that Gnome/Unity/others(?) remove settings like that.
Anyway, looking around the web I found the solution. The middle mouse butten emulation can be enabled in the Gnome configuration by running the following in a terminal:

gsettings set org.gnome.settings-daemon.peripherals.mouse middle-button-enabled true

It worked immediately!

As an aside, I also had to install the packages nvidia-current and nvidia-settings in order to use the nVidia drivers. Without them using the Unity interface was dead slow, even though the laptop has an nVidia Geforce Go 7400.