There's a lot of people out there who think they should be able to get videographers to work for free. Just check the craigslist job board right now and I'm sure you'll find a couple. Many people are positive that the "exposure" you'll get from doing their video will be so valuable that videographers should be groveling at their feet to be a part of their project. Well sorry! If you want professional results, you're going to have to pay for it.
But I'm not one of those absolutists who will rant against craigslist postings (here's an example from just this morning)...
...and there are times when I will work for free.
Last month I shot an interview with Justin Carder, for Daisy Whitney's New Media Minute. I didn't get paid, but in this case the exposure was definitely well worth it. My website got screen time in the video, I got a link in all the places the video was syndicated to (including the Huffington Post*), and most importantly, the show is targeted at people interested in New Media, exactly the kind people that it would be valuable to get my name in front of.
So while I would, in general, recommend against working for free, there are definitely times when working for free can be a good business decision. Just make sure that the exposure you'll be getting is worth the time and effort you put in... and remember that most of the time, it's not.
Here's the episode. She introduces me/ my interview at about 1:12.