I feel your pain guys. I likewise preordered very early (April 1), and am still only seeing a "Ready for UPS" message. I don't think T-Mobile is giving priority to people who preordered later. I haven't tabulated all the info people have given here, but qualitatively I'm not detecting any correlation between order date and time of (actual) shipping.
Really though, I'm not that bothered about all this. When I saw that message on my.tmobile.com the first week of April stating that my phone would only ship between the 20th-21st, I was pretty disappointed that I may get my phone a full day after it's available in stores. Now it looks more likely that the latest I'll get it is on the launch date. So it's looking better than it was two weeks ago!