Hi
It's not immediately obvious here, to be sure.
You have to have Address Book OPEN and have selected the contacts or groups you want to export.
So, I have Address Book open, and I've selected the "Holiday" group, and then in the Contacts pane, Select All
(Apparently just selecting the Group does not work, although one would think it should, if you were to change the option in the "Get Selected" tool)
Once all your contacts are selected, you can run the workflow, as shown and get a text doc with all the data as a tab-separated (spreadsheet) or text formatted (data per line) file.
So, it does not convert vcf FILES but converts the DATA for you.
In other words, don't bother exporting the vcf files from Address Book!
Hope this helps!
& Thanks to Barney for the tip!