Does Google Assess Spelling & Grammar for Page Ranking?
In this video Google’s Matt Cutts answers a question from AJ Kohn (AKA “blind five year old”) about an issue that’s caused no end of speculation in the SEO community.
The tl;dr – Matt says last time he checked the answer is “no” but…they have noticed a high correlation between pages with few or no spelling errors and pages with high PageRank. Matt attributes this to the probability that people who care about producing good quality content probably also care more about things like spelling and grammar.
Matt also discusses the inherent difficulties that trying to automatically evaluate spelling and grammar would present.