Yep.
It's a great entry level recorder and system with a plug-in mic when you're doing mosty DIY one-man-band sort of stuff.
Obviously, at some point (hopefully) the quality of your work will create financial demand to justify the usage of a PSM (
http://en.wikipedia.org/wiki/Production_sound_mixer) who will have a real live field mixer set-up and know what to do with it.
http://www.bhphotovideo.com/c/searc...&N=0&InitialSearch=yes&sts=ma&Top+Nav-Search=
However...
In the meanwhile...
Back to that DR-40...
Pretty much any recorder over a $100 (US/AUS/NZ) is going to be better than what you're going to get off your camera.
Fact.
Use it's own mics for ambiance audio and controlled interviews.
Use a mini jack plug in mic for a good bit better audio collection options.
Use a XLR jack plug in mic for even cleaner recordings, less static.
Look for "low impedance" or low Z mics and cords.
https://www.google.com/search?q=low...H4AQ&ved=0CAkQ_AUoAQ&biw=1745&bih=882&dpr=1.1
Just remember: You can't tech your way out of a crappy film.
The problem with most films is somewhere between FADE IN: and FADE OUT:
http://www.indietalk.com/showthread.php?t=44510
Bonus!:
You can even get a dead cat for your DR-40.