There are LOTS of talentless actors out there that have captured large audiences. The MySpace personas definitely fit that, but I am sure if you put your mind to it you can come up with a lot of hacks that have had their 15 minutes of fame over the years.

Tyra Banks as a talk show host comes to mind.
That guy that lived with OJ.
Eddie Murphy trying to sing [remember 'Party all the Time'?]
ALL reality shows
NASCAR