Timothy Armes has announced the release of PLUS for Lightroom: a plug-in for embedded PLUS usage rights when exporting images from Lightroom 2.
The PLUS standard is becoming recognized as the way to specify usage rights for digital media works (see http://www.useplus.com).
Some of the editors supporting PLUS are McGraw Hill and Pearson.
The trial version of the PLUS plugin is available here http://photographers-toolbox.com/products/plusforlightroom.php.