Say for example that I wanted to play a song by that great band from Guelph, Ontario, The Kramdens. With spotlight, unless I can actually name the song, I'm SOL. Typing "kramdens" into spotlight reveals only files and directories with that name.
But with Windows 7 (Vista and XP as well, actually) my search tool has indexed not just the file name, but also all the mp3 tags. So I not only see the folder named Kramdens, but also all the songs on my computer that are written and/or performed by The Kramdens. I also see the names of folders that contain albums of their work. 
I tried the same experiment with the Dock/Spotlight tool that Mac-heads seem to be raving about called QuickSilver. The results were even worse. It doesn't seem to be indexing my portable drive at all and finds only the images I saved in preparing for this post.
