The wealth of applications on a modern Linux system is phenomenal, but sifting through screen after screen of menu items is no fun. Likewise, it's convenient to have all of your files in one place, but the more you have the longer you have to look for the one you need.
Blacktree software's free Quicksilver Mac OS X utility won over users by letting them start typing the name of the file or app they need, and popping up the best matches in a launcher. Quicksilver went open source recently, but you don't have to wait for a port to start using it on your Linux machines. Two clones already exist: Katapult for KDE (which we looked at in July) and the newest competitor, GNOME Do.