I'm a native English speaker who can sometimes go all grammar nazi, and I hate it when people mix up their/they're/there, etc. That being said, most of the time people who do this are also native English speakers. People who have English as their second language generally don't do that as often.
I don't mind as much if something is written well and is understandable, even if it's clear the person who wrote it isn't a native English speaker. In those instances, it's generally small things like word choice and sentence structure that give it away.
Disclaimers never bother me, though.