I had seen an article on Ubuntu HUD recently and finally got a second to actually read a little about what it does. The idea seems to take the use of tools such as Quicksilver or Alfred and apply the same workflow to menus actions in all applications. Overall it seems like a slick idea. The video in the post above shows how it can be used on the command line! Very nice.
My biggest question is that of discoverability. I remember when I was working on the NLD 9 usability and felt the push for search was somewhat misguided. Search is extremely powerful, but it is also something of an art form. As a programmer, many times my goal in asking questions in forums or on IRC is to gather new terms to help aid in my searches. When you are a young programmer with no formal training trying to understand how to work with files, knowing terms like “handle” or “EOF” can be tough to discover on your own.
What is easy to appreciate in the HUD idea is that you never need to leave your keyboard. This is the reason I’m enamored with Emacs. It provides an interface to do so many things, that you rarely need to leave the comfort of your frames and buffers. In Emacs the use of plain text enables this sort of tool to work and I’d assume that GTK+ (more or less) is what allows HUD to take things like menus out of the application and add them to an index. If this assumption is correct, we might finally see how a free platform has an advantage in providing a better user interface. I doubt you could ever see such a widespread conceptual change in something like OS X or Windows, partially because it may not make sense to users, but also on a technical level it seems really difficult.
No matter the long term effects, it is exciting to see some innovation in user interfaces that reflect the maturity of the “computer” as a tool that the majority of people use.