It is possible to introduce ambiguity by means of an Oxford comma. Taking Maryn's third sentence above:
Highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector
If you add the Oxford comma in, you remove Mr Mandela's dildo collection from consideration, but then the phrase an 800-year-old-demigod could be an appositive describing the famous South African.
Basically, you should check your comma-delimited series for the possibility that they can be misread as appositives. Both of the below sentences are unclear.
I would like to thank my parents, Ayn Rand and God.
I would like to thank my mother, Mother Theresa, and the Pope
Sometimes the best solution is to rephrase; sometimes it's to add or remove a comma.