Duane Forrester from Bing strongly implied on the Bing Webmaster Blog that having poorly written content with poor grammar will have a negative impact on your search rankings within Bing.

Duane wrote:

It seems like Bing is judging your content based on your grammar.

Google, well, not so much. Google doesn’t care if you have bad grammar in comments and said in 2011 grammar is not in ranking algorithm – yet.

But either way – having poor grammar may upset your users and push them away from your web site. Which can have a long term negative impact on your search traffic.

Forum discussion at Google+.