All messages will be delivered to them, granting that you send it to the correct username.
There isn't any way of knowing. If your tweet contains their username then it will definitely appear in their @replies.
Yes, you can actually know if someone retweet or mention you in twitter. It is a default feature in twitter and every tweeple (twitter people) can know who followed and mentioned them.
because it let you know if you got a e-mail on twitter
There is no way of knowing this.
They will tweet about it.
No there is no way for anyone to know who has viewed their profile.
Yes! You can look at anybody's Twitter page, and they do not know who's viewing there page. No worries
You can't know, unless you look in their favorites.
It will appear in the connections tab.
search them on the internet: eg facebook twitter etc
On Twitter, @MattHardyBrand. Other than that, I don't know.
If you know their log in details.
When you reply to someone (and therefore their username is in your tweet) it will appear in their 'mentions' tab (the @username tab on the right hand side).