The Daily Show's Samantha Bee really nailed it about why McCain chose Alaska Governor Sarah Palin. (Also, Fox News's Steve Doocy is a true moron. EPIC GEOGRAPHY FAIL.)
Stephen Colbert also highlighted the hypocrisy and cheap political ploy of it all.
Now, as for who Sarah Palin really is, BoBo2020 lists 45 different problems with Sarah Palin, ranging from scandals she's involved in, dangerous policies she espouses, recent gaffes she's made, to her radical right-wing beliefs. The biggest problem? She's a global warming denying, pro-ANWR drilling, pro-life even in the cases of rape and incest, Dominionist movement belonging, creationist loving, oil company shill.
As for why McCain picked her, this video may offer some clues. Turns out McCain's Brain was also miked during the rally introducing her.