At least with 'then' and 'than', there is the excuse that they are phonetically interchangeable in some accents so could cause people to write it as they say it. (Although it does piss me off just as much as it does you)
Aside from the subject matter itself, has anyone noticed the sudden prevalence of people using the plural 'women' when they mean 'woman'? Does my nut in.
"I confronted a Muslim women yesterday in Croydon. I asked her to explain Brussels. She said "Nothing to do with me". A mealy mouthed reply."