I found this thread just before going to bed and it's grown to 3 pages, plus a Best Answer, by the time the day was done.
I'm still bugged by how it was *technically* achievable for any person, or (sinister?) lurking computer code to find and follow her account in 5 seconds.
@Bathsheba, was "5 seconds" just a figure of speech or do you mean literally?
I signed up on my laptop and vaguely recall a fair old pause after pressing the big button to create my account, before I could even look around to see what the newsfeed page looked like, so 5 seconds would be about as long as it would take to work out where to click before you could start typing.
Until this year (or some time in the last 12 months), you were "discoverable" on Twitter, via other users searching for the email account you used to sign up with. If your real life friends know you're not the kind to run multiple emails, disguised names etc. then they'll not have a hard time guessing which account you signed up to Twitter with. But it would take a real tech-head to write a script to scour Twitter continuously until you signed up with an email they know.
To anyone else, I think you're invisible on Twitter until you make your first Tweet. If you run a search for the phrase "this is my first tweet" or "hello twitter" you might be able to similarly spook someone who signed up seconds ago.
Other than that, there is the problem of the many namesakes we all have. If I search my actual name in Facebook, I have about a dozen.