Scott Beale just posted about ZingFu ignoring his CC license and using one of his photos for a promotional card without either asking (which is required for commercial use) or crediting him. This happens to me rather frequently, which is why I've borrowed (with permission) the wording that Scott uses on all his photo on flickr:
This photo is licensed under a Creative Commons license. If you use this photo, please list the photo credit as "Scott Beale (Laughing Squid)" and link credit to laughingsquid.com.
Of course, I've replaced his name and website with mine, but I am guessing from his results, this will still not be enough.
The last two entities to refuse to properly credit my photos, and thus violate my creative commons license, were NPR and the Flickr Blog. I have also recently been contacted by an editor on Wikipedia, who has asked me to change my license to allow for commercial usage, which I will not do by any means. I find it very unfortunate that Wikipedia forbids -NC CC photos, but here is a page in support of their reasoning.