Would having some flaws in a perfect English SOP be bad?
From the survey Kisses of Death in the Graduate School Application Process by Drew Appleby and Karen Appleby:


  According to several respondents, spelling and grammatical errors found anywhere in the application are an immediate Kiss of Death.


My job should finish here, but I want to summarize the paper after a quick skim. 5 major Kisses of Death are:


Damaging personal statements: personal mental health, excessive altruism, excessive self-disclosure, and professional inappropriateness.
Harmful letters of recommendation: undesirable applicant characteristics, letters from inappropriate sources
Lack of program information: not researching the general focus of the program, not exploring how the applicant’s research interests fit the focus of the program.
Poor writing skills: spelling and grammatical errors, poorly written applications
Misfired attempts to impress


Thanks Roger Fan for linking this survey.