One goes not see this mistake regularly, but one will remind oneself to keep an eye out for it. 
Of course, there’s nothing wrong with terminal prepositions (as a general rule. I’m sure you can come up with constructions where it would not be ideal.). I doubt there are many, if any, prescriptivists/stylists around that object to it.
2.3 percent of the time, it seems to myself.
You know what really grates? When people say pied instead of pes, frère instead of frater, and act like their language has only two genders. They aren’t speaking correctly, and their utterly barbarous sub-literate ape-hoots are all that is wrong with society. How can you keep fides when you think it’s foi, I ask you? How?
Don’t talk to me of Larousse. He will be first against the wall when it all comes apart. His perversions haven’t gone unnoticed. I’ve made a little list, oh my oui… damn!
An example I recall would be something like: Where are you going to?
In that case it’s not really because “to” is a preposition, but rather that the word “to” is not needed at all.
But your point remains that we are presumably discussing English as opposed to Latin.
People also say “Me and X (insert verb here)…” even though “me” is the direct object (we call them “accusatives” in Latin)
You’re right that I is supposed to be the subject (“I did this…” or “X and I did that…”)
And then there’s the former coworker who referred to “you’s guys’s cars’s gas tanks”. It was a setting in which correction was permitted, but I didn’t know where to begin.
“Youse guys’ cars’ gas tanks,” of course. 
(Actually, a serious answer if you want to keep the colloquial with proper apostrophes.)