Operating systems and applications need to support a mode wherein typing the smallest identifying subset of keys will cause the appropriate file/function to be opened. Firefox 3 does this for history urls - start typing and you'll see URLs that contain that set of keystrokes anywhere in them. iPhone's safari also does a decent job. Adium does a basic version: you can hit apple-N to get a New Message window and type the start of the person's name. I think Quicksilver also does this although I've never been able to make heads or tails of it.
Every application should do it. Eg. Eclipse - it's silly for me to go hunting for the file I'm looking for in the tab + drop-down list of files I'm editing. I should be able to hit Ctrl-Something and start typing some piece of the name of the file and it should show up.
On the command line - it's silly to type in the full path to get at the directory I want when it has a set of uniquely identifying (or at least narrowing down) set of keywords.
In adium, instead of showing only the contacts that start with what I'm typing, show contacts that have those characters anywhere in their name. How am I supposed to know Max's id is crazymax2007 ? I just want to type max.
In short, I should be able to hit some hot-key combination, type a few letters, and get access to the most common functions and files that are identified by that set of letters, from every application.