When I am meeting with any professional, especially one with far more experience in a field than I have, I expect a certain level of competence. To me, being able to communicate well is nearly as important as the final product or overall service a person provides. For this reason, when someone begins speaking, and in doing so, sounds like an elementary school student who has not completed one single grammar lesson, I start to get nervous. I worry that without the basic ability to speak well, the professional in question may not be able to produce high-quality results.
As an example, I was looking into different options for flower arrangements recently. When I expressed to a particular florist that I like simple elegance, she responded with, "I seen something you might like." At that moment, I was almost certain I would not be ordering flowers from this florist. While I understand that the use of proper grammar probably has little to do with her ability to create lovely floral arrangements, I simply could not look past the poor grammar. In my opinion, poor grammar is distracting. I have trouble ignoring it, frankly.
Maybe I'm just a snob for proper grammar, and I definitely appreciate someone who is well-read enough to understand my literary jokes, but I struggle to take someone seriously who is speaking to me without a hint of grammatical intelligence.
I also flinch when commercials air with lines like "less calories" or "less miles." Companies spend millions of dollars on advertisements. Why, then, does it seem that they are so resistant to hiring an editor?
The same is true about the use of punctuation, by the way. As I demonstrated in the example above, a comma placement can make all the difference.
Come on, people, get it together. Use grammar well.