Here is a Slashdot post I went to the trouble of composing. Copernic Search is pretty good and here is why:
Advantages of Copernic:
1. Google desktop search is strictly not for commercial use (For commercial use, you need to buy a Google appliance) (I wrote to them to find out if this prohibits any use in a commercial setting such as on an employer's computer and they did not reply)
2. Google desktop search does not index PDF files
3. Google desktop search does not do partial word matches (huge disadvantage when you have filenames which are just concatenated words with no spaces)
4. In GDS, you get to exclude folder that you do not want to index, in Copernic, you get to include folders that you want to index. I prefer the "index only when asked to do so explicitly" option.
5. GDS will not index mapped network drives except for files that you actually open and use after installing GDS
6. Unlike GDS, Copernic will index outlook email attachments also
7. Copernic gives a real time preview of the matched area as you highlight each search result line
I am sure GDS will be a great tool someday. For now, Copernic offers better options. And now that GDS is here, Copernic is free! Competition is always good for the end user!