Very nice work here, esp for free! I needed it to combine multiple jpgs & pdfs into a single PDF that I could fax all in one shot instead of having to send multiple faxes.

The only nits I have are:
1) Some kind of progress indication would be nice.
2) Should be able to disable the autolaunch of Preview upon completion. I prefer to use the much faster PDFViewCM (http://www.versiontracker.com/dyn/moreinfo/mac/21004) to check the results.
3) I tried to combine several JPG files (8.5"x11", 200 ppi) and a couple of PDF files (8.5"x11", 300 ppi) into one PDF, and the scaling wasn't quite right. I ended up making 2 PDFs instead of one giant one.

Overall, very very good though! (Esp considering the price. :)