Percentage as plural
From the WSJ today also came this sentence:
Weeding out youngsters is critical in accurately calculating one of the valuable bits of data ShopperTrak sells -- the percentage of shoppers that buys and the percentage that only browses.
While percentage technically is singular, as Bryan Garner notes, it usually is construed as plural when followed by an "of" phrase that uses a plural object. There might be some debate here given the sentence construction (one referring indirectly to percentage). But this would sound less tinny and be more acceptable if recast to: the percentage of shoppers who buy and the percentage who only browse. (Who also is also preferable here, as it more correctly links "buy" to "shoppers" not "percentage." "Shoppers who buy" is really the complete object of the preposition.)