When confirming wether faces recognized by iPhoto '11 are actually correct, some will be wrong and need to be rejected.
iPhoto gives the hint to 'Click to confirm or Option-click to reject,' yet the easier and faster way to reject would be to simply double click the image, after which it will be marked as 'Not (name).'
[crarko adds: I tested this, and it works as described. Yet another undocumented feature of iPhoto.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=201102201022494