I've heard sentences such as "I, too, did something," in which I would have used "I also did it," or "I did it as well," or "I did it, too." In school I've been taught I have to put 'as well' and 'too' at the end of a sentence and 'also' after the subject. Was I taught correctly or do those rules apply only on a case-by-case basis? (I don't mean 'me too,' which isn't wrong, but informal).
To my ear, "I too did it" and "I did it too" are very similar in emphasis. The former leaves the stress on "too," whereas the latter stresses both "I" and "too," reminding the reader of my particular role.
This is quite subjective, but I hear "I did it too" as being somewhat plaintive, as if it supposes that someone has forgotten me. (I'm reminded of my younger sister's "me toooo!" Which is to say, "don't leave me out!")
While we're at it, let's not forget "I did too do it," used to counter an accusation that one in fact did not.
A schoolyard classic: "[You] did not!" "Did too!"