The good people at PolitiFact have checked her claim that Obama often voted present when he served in the U.S. Senate.
Oh—that evil Obama. Always pulling the wool over the eyes of the unsuspecting public. Except, of course, he didn't.
PolitiFact concludes with a definitive statement:
Palin's statement is incorrect in two ways. She initally appears to suggest that Obama had only 150 days of experience in the U.S. Senate, which is inaccurate. She then says he voted present many times, which also is not correct. He never voted present in the U.S. Senate. So we find her statement False.