Calibre is one of the most popular converters out there, but there are many more if you google "PDF to ePub Mac". Be sure to check if you need to. May eReaders these days support PDF as well as ePub.
What's more, you may try this tutorial about how to convert PDF files to ePub on Mac. Results depend entirely on the PDFs that you want to convert.
Glad that you got it working.
Edited by sinajiun - 07 October 2011 at 8:03am