Since I learnt about the Creative Commons a few years ago I have my Flickr set to mark all my photos as cc-by-sa (By Attribution, Share-Alike). Now I don't have much to lose by doing this since I'm not a professional photographer and my only goal in uploading my photos is to have people look at them, which the CC license has certainly helped with.
Probably the most gratifying Creative Commons related experiences I've had were from various authors asking permission to use my photos. One of them has been published in the 50+1 Malaysia Book.
I was also contacted by a girl in Italy who was looking to publish a book about France, and wanted to use my photo of Tripe alamode de Caen. Unfortunately this project didn't pan out but it turns out that the same photo has been used in Wikipedia in the article about Sidoine Benoît, a Benedictine monk of the 14th Century. Had I not licensed this photo under the cc-by-sa license I would never have realised the history behind this dish.
I also had a strange experience with a marketing guy in Malaysia wanting to buy two photos of hawkers for use on a micro-finance brochure. This presented me a personal dilemma as both photos clearly showed the hawkers' faces and I wasn't sure if they'd necessarily want to be associated with whatever bank was running these ads. I read some stuff about model clearances and decided that ultimately if it was me in those photos I probably wouldn't want to be associated with no bank. So I replied suggesting that if marketing guy could find those hawkers (which wouldn't be difficult as they have a regular location) and get their approval I'd be happy for my photos to be used. I never heard from marketing guy again.
Looking through my Flickr stats it turns out a number of my other photos have also been added to Wikipedia - in articles about Pisang Goreng (a type of banana fritter common in Malaysia and Indonesia), Baked Alaska (a fancy looking dessert), Almond meal, and everyone's favourite fruit - the Durian.
By literally doing nothing more than just a few small clicks to use the Creative Commons licenses I'm contributing to the world's knowledge, how cool is that!? You should do your part. :)