A great idea, however it took only a few minutes to work out that by typing a 5/6 letter name into the short code field, the chances are high that it will relate itself to a user - I tried 10 names, 7 of which are real users.

While I haven't (and won't) misuse the premise of Tsu, others certainly might. Security is a big deal, and at first glance this does't seem to cut it.