I noticed that mdfind has become much more useful now in Leopard. For instance, you can run Finder saved searches from the command line. As an example...

mdfind -s "Pet Pics"

...will show the results of saved search called "Pet Pics." It actually looks for the saved search in ~/Library/Saved Searches, but you can give it a full file path if you wish. This means you can build up your queries visually using Finder, then easily use them in scripts. Also, you can give mdfind queries in the same language that you'd use in Spotlight:

mdfind -interpret "pet kind:image"

As usual, check man mdfind page for more info, but note that the man page is not consistent with all that mdfind can do (eg, it doesn't mention -s in the man page).