When you hit the rate limit, you should get some sort of HTTP error, and not a valid return (at least thats what I was lead to believe).
As far as a "tweet" limit, there isn't a limit, but your followers might get angry and annoyed and unfollow you. I don't know what your purpose is though. If your tweets are too similar, they might not be posted again, as we have brought up before in discussion. By "tweets are simply not being allowed for a user" what do you mean? HTTP Error? Sending a Tweet via API and it not being correctly displayed via the website and/or API?
