The Automator workflow I used in Tiger no longer works in Leopard. If you use more than one "Move Finder Items" or it is not at the end of the workflow then you will notice an error if no files are passed to it.
I had three "Move Finder Items" with filters before each.
In Leopard, the Move Finder Items errors. It would be nice if they added an option for it to error or not, but they did not and it broke many peoples workflows.
My solution is to use Run Shell Script in place of Move Finder Items.
Add a Run Shell Script and remove the Move Finder Items. Set the Run Shell Script as argument.
Paste the below into the Run Shell Script.
for f in "$@"
mv "$f" ~/folder
Change the folder to the location you want to have items moved to. The ~ indicates that is the your user folder.
For example, you might have a PDF folder in your user folder and then want to move all PDFs to that folder. Just put ~/PDF then make sure your filter finder items has name extension contains pdf.
Please post a comment and let me know if this has helped you.