A young friend who consistently and erroneously uses "then" instead of "than" in her Facebook posts just used "than" when it should have been "then".
My head exploded a little bit.
"Than" indicates an unequal comparison: Jan is skinnier than Carol.
"Then" indicates order in time or place: I am going to work, then to the grocery store. To get to my place, you pass the QuikTrip, then the Post Office.
These aren't even homonyms, like the "you're" and "your" confusion. Or "their" and "there". Honestly people, for the sake of the grammarians in your lives, learn the differences.