I heard the commentators say (after Mayweather got cut against Maidana) that this was his first cut ever. I remembered he had a fight against a southpaw earlier in his career - watch this video at time mark 12 minutes:
http://www.youtube.com/watch?v=pgCshY_8Huk#t=12m
http://www.youtube.com/watch?v=pgCshY_8Huk#t=12m