First, begin your search in Macintosh HD, or select "This Mac" rather than "All My Files". If it's not finding things you know are there, try re-indexing your drive:In Snow Leopard, whenever I typed in a word, e.g SuperDuper, it would find it, but in Mountain Lion, it doesn't, why?
https://www.dropbox.com/s/k9jf2wd9get76z5/Screen Shot 2013-04-27 at 10.06.11 AM.png
If that fails to index, enter the following command in Terminal:
sudo mdutil -i on "/Volumes/your drive name"