This user thinks that there are too many people who don’t know that they're worse than their own children at spelling!
they he or she
This user considers the singular they to be substandard English usage.
your you're
This user thinks that if your grammar is incorrect, then you're in need of help.
’s
Thi's user know's that not every word that end's with s need's an apostrophe and will remove misused apostrophe's from Wikipedia with extreme prejudice.
its & it's
This user understands the difference between its and it's. So should you.
This user has no opinion about ending a sentence with a preposition.
A note on prepositions. I consider a sentence which ends in a preposition to be poorly phrased, but note that in my opinion many prepositions in the English language are really parts of multi-word verbs. In my view of English grammar, in the sentence “He dropped in on her.” only the word “on” is truly functioning as a preposition. I consider “dropped in” to be a verb with a meaning distinct from that of “dropped”. I don't think most grammarians agree with me, but I think my view makes sense.
The idea of a verb which is made up of a verb and a preposition can be compared to the many Latin verbs which are formed from a preposition and a verb: referre, retinēre, accipere, ascendere, etc. We simply haven't combined them into single words in English, in these cases. (But note that we do commonly use Latin or Greek prepositions as prefixes on English verbs.) So while I try to avoid ending a sentence with a preposition when the preposition is not part of a verb, it's quite acceptable (and very often necessary) if the preposition is functioning as part of the verb, as in the sentence “We had no warning that he would drop by.”