I think we've all heard of these things... but I'm sure these people are few and far between... I think anyone trying that is quite stupid, because if you got caught out the reprocussions are pretty harsh and if you were to do this on the 15 odd exams (7 CPL, 7 ATPL & IREX) you're really wearing down your odds.
These people also will unlikely pass an interview when they get asked stuff about say AIP 1.5, and are ripping themselves off if they don't know the in's and out's of duty times. Not to mention possible incorrectly loading an a/c and turning themselves in to a lawn dart.