Just 20 seconds to advertise the command line a bit.
To open or close the command line window in Dolphin file manager press F4. To auto-finish file names press TAB. The syntax is pdftk inputfile1.pdf inputfile2.pdf cat output outputfile.pdf. Not hard.
If you can do the same thing on a Mac, let me know.
(You are looking at pdftk on openSUSE 12.2 with KDE. Recorded with XvidCap Screen Capture edited a tiny bit in Avidemux.)