Phd,
Just to be clear, I'm as far from a PhD as can be. I also make frequent spelling and grammatical errors. I think that I am overly sensitive to the frequent misuse of "there" and "their".
If you take notice, many posters use the two words incorrectly every day, most commonly using "there" when they mean "their". It's surprising how often it happens, even in printed reviews!
It's equally surprising that the error is most often made by posters whose first language is obviously English.