If you are feeling desperate to try this out, you need to have Ubuntu 12.04, add ppa:unity-team/hud PPA to software source and run update.
Heads Up Display (HUD) is what Mark Shuttleworth calls this new menu mechanism. And no, it’s not going to replace existing menus. Imagine HUD as this. You are working on a document and you want to print the document. Instead of clicking on nested menus to print, you just need to type ‘print’ and you get the options for print. And the results are displayed dynamically as you type (known as look-ahead-search). In short, you type what you want and the right menu options are displayed on your screen. The more you use HUD the better the filter will be, thanks to ‘fuzzy matching’ technique.
“We’ll resurrect the (boring) old ways of displaying the menu in 12.04, in the app and in the panel. In the past few releases of Ubuntu, we’ve actively diminished the visual presence of menus in anticipation of this landing. That proved controversial. In our defence, in user testing, every user finds the menu in the panel, every time, and it’s obviously a cleaner presentation of the interface. But hiding the menu before we had the replacement was overly aggressive. If the HUD lands in 12.04 LTS, we hope you’ll find yourself using the menu less and less, and be glad to have it hidden when you are not using it. You’ll definitely have that option, alongside more traditional menu styles.” said Mark Shuttleworth in his blog.