This was debated back on the old boards. It was decided that anonymous rep was the way to go.
If people could see who gave them rep, then giving rep might cause you to get the same rep back. This would have a bunch of problems :
(1) People who gave out +rep would get +rep back, even if they diddn't deserve the +rep they got back.
(2) People might try to increase their rep by giving out lots of +rep for not-very-good reasons, and counting on others to give them +rep back even if they don't deserve it.
(3) People might stop giving out -rep, even when it was justified, because they feared the other person's response.
(4) People who do give out -rep might unintentionally (or intentionally?) cause a fight with the person they gave the rep to. This could lead to negrep wars and drama.
(5) Making rep non-anonymous would result in more rep being given, meaning more rep for me to check.
(6) Currently, people have a choice about whether they reveal their name or not when they give rep (though, doing so is discouraged, they can still do it). Why force someone to identify themselves when they don't want to?
(7) What about the people who gave rep in the expectation it would be anonymous? Is it fair to change the rules on them now?