Remember back when Steve Jobs introduced us all to Spotlight. He did a demo that seemed like magic. He typed in a word and Spotlight found audio, video, photo and text documents related to that word. I was amazed and rushed to get Tiger installed on my mac. What a let down when I realize that this only works if you have tagged your files with Spotlight comments. That can be tedious to do. Normally you have to select the file, get info on it, then type in the tags and close the info box. With some basic Quicksilver skills, you can automate this process. Here is the documentation for the Tagging plugin of QS.
The only modification to this tutorial is to select some files to tag and then invoke Quicksilver. You can do this by navigating in the finder and selecting the files you want tag. Invoke Quicksilver (ctrl-space) and hit that super secret key combo cmd-g to bring them all into Quicksilver. I'm pretty sure that this is the fastest and easiest way to add Spotlight comments.