The rules as currently presented state that a character may not exceed 20 in any ability. While I like that character can not naturally move past 20 like in 3.x I am not a huge fan of this because I feel that it takes away something special about playing a race other than human. I like the idea that an elf has the potential to be more dexterous or a dwarf tougher than a human can ever be naturally. I figured that they would cap out characters at 18 before magic to make 18 the baseline and other races cap at 20 on their increased stats. I am also a fan of other races getting penalties to offset their higher stat but I understand that there has been a shift away from penalties.