Spotlight loses index of Applications
This happens whenever I erase the free space on my hard drive (probably for the same reason -- that process creates a big file that eats up all the free space, then overwrites it, creating a low space condition in the process).  Typing this command at the terminal:


  sudo mdutil -i on /Volumes/Hard_Disk_Name_Goes_Here


will rebuild your index. Substitute your own disk's volume name in the obvious place.