You have probably figured this out by now, but for reference here is how to get the functionality you mentioned. The Logitech Performance MX 950 is also called just the Performance MX in some markets, so these instructions work for both the "Performance MX 950" and "Performance MX" models.
Setting up Zoom and Window switcher buttons
Install the CompizConfig Settings Manager
sudo apt-get install compizconfig-settings-manager
Open the settings manager, either through the Unity menu or by typing
ccsm in a terminal.
Go to the "Scale" plugin. Under the tab "Bindings", assign Button 10 to "Initiate Window Picker For All Windows" by clicking on the button in the row with the mouse icon. This will give you the spread windows functionality, using all windows from all workspaces. If you prefer to just see the windows from the current workspace, instead assign the "Initiate Window Picker" shortcut.
Go back, and open the settings for the "Expo" plugin. Assign Button 13 to the "Expo Button" setting. This will give you the show workspaces functionality.
All the other buttons should work out of the box in Ubuntu, at least they do for me with Ubuntu 14.04. Do not be tempted to change any other settings in
ccsm, as you can easily break your system with it.
Additional tip: You can run
xev in a terminal to see exactly which buttons are currently pressed.
Setting up Solaar for additional settings, and managing the Unifying receiver
To manage the Unifying receiver and change a few settings on the Performance MX (scroll sensitivity, DPI settings), you'll need to install Solaar:
Add the PPA:
sudo apt-add-repository ppa:daniel.pavel/solaar
Update your sources:
sudo apt-get update
sudo apt-get install solaar
Run Solaar from the Unity menu. To make it work for the first time, you'll need to unplug the receiver, plug it back in, and turn the mouse off/on.
Solaar will run in the background and show a small indicator in the top menu bar (next to the Wifi indicator). You can configure your devices or quit Solaar from there.
Solaar will add itself to the Startup Applications, which will make it start automatically on login. Personally I find the battery notifications distracting so I have disabled the Solaar entry (just remove it from the Startup Applications).