Usually you don't want to change letter spacing. It should be part of the font itself. By changing it via CSS letter-spacing, you alter the font's built-in spacing. This is particularly noticeable with letter combinations with very tight kerning, like 'AV' or 'WA' or 'li li' or 'ni in'. While most web fonts do not have the vast kerning tables that a professional typeset font will have, the built-in kerning is usually leagues above what you can accomplish with letter-spacing.