As most things in Linux land, this can be modified. And of course this can be done in various ways. To make it easier for non-Linux/Ubuntu guru we will try to do this via CompizConfig Settings Manager (ccsm as this is the name of the python script).
Unfortunately this is not installed by default but this is so easy in Ubuntu. Again this can be done in various way but will try to do this in Ubuntu Software Center. In Software Center search box type ccsm. Select Advanced Desktop Effects Settings then follow instructions to install it.
Now run ccsm (using console/terminal or using dash). Select Desktop category then select Ubuntu Unity Plugin.
Figure 1. Ubuntu Unity Plugin
In Ubuntu Unity Plugin, change Key to show the launcher to desired key sequence. From Figure 2 below it is changed to <super>z (Windows Key + z).
Enjoy playing with Unity!!!