I always appreciate the clarification of proper use of grammar, but when it appears in article comments and forum discussions, I've always found it to be more offensive than the error itself. This is mostly due to the "I'm smarter than you" attitude used to convey the message.

I very much appreciate anybody, anytime pointing out my grammatical errors. How else will I learn?

The "smarter than you attitude", imho, is usually self-inflicted because we feel silly knowing we should know better.