Follow the links in a MacSlash story about web badges, I ended up skimming Apple's Guidlines for Using Apple Trademarks and Copyrights, and noticed the following, fairly broad, prohibition:
3. Variations, Takeoffs or Abbreviations: You may not use an image of a real apple or other variation of the Apple logo for any purpose.
"Any purpose". Thousand's of unimaginative still-life painters must be quaking in their boots.