The article says, regarding community-developped fonts like Linux Libertine and DejaVu, that «The perception among the public is that the commercial fonts are of higher quality than the community-built fonts».
Does that perception really exist for Linux Libertine? It's one of the most beautiful general-use fonts that I know (including for-pay fonts). I've typed in whole books in it and loved it. Its italic characters are particularly nice and subtle, and I've heard people express admiration (without knowing what font it was, or that it was free).
Liberation Serif is also looks quite decent, but I'd say it's not quite so elegant,with those big pointed serifs and the pointy hook of the lowercase 'r'.