Wow guys, this sounds really bad. I thought that the flaw is simply that the signal is weaker by half (as it is on my tests), but apparently it doesn't get any locks at all for some of you.
This is definitely not a metal casing problem, GPS antennae seems messed up. GPS, by design, should get some locks after just a few minutes, no more than 10 or 15 minutes.
All of my tests show the flaw of metal casing weakening the GPS signal, but it still finds satellites (though cannot be used for navi as a result) without WiFi.
Try going to some open space and hold the tablet skyward and see if there's any change. Indoors is not an ideal testing condition (depends on where you live), because it still might be the metal-back issue.