I've been trying to read into this screen lifting problem since I noticed my N7 making a noise and feeling like it shifts slightly. This is one thread I read throughout. I'm trying to get an understanding of just what it is and the seriousness level.
If I hold my N7 in landscape mode two-handed, holding it like a small portable game system similar to nintendo DS, when I push up any on the back of the tablet I hear a small creaking noise.
Or if I hold it one handed resting on my palm and press down on the touch screen again I hear the creak.
Does this sound like screen lifting and is there a danger of this becoming a bigger problem?
The screen lifting is just that - the screen does not seat fully down into the bezel that surrounds it. In more extreme cases like mine (a first-batch C60 model) you can push down gently on the middle of the left side of the screen and feel the glue re-adhere, then feel it release with a click or pop sound. Even though the lift is extremely subtle, in good light you can look at the device side-on and see glass protruding above the bezel, where in reality the top edge of the glass should be even with the top edge of the bezel.
As to the chances of it getting worse - I can only say that my device is about the same as the day I bought it back in August. There's no sign of it getting any worse, and with any luck my 10Terra bamboo case that I ordered during their Kickstarter campaign will FINALLY arrive in a few days. Once it's in a case that keeps me from obsessively pushing down on the loose bit, I shall worry about it no further.
I'd look carefully at your device, and particularly on the left side as you hold it in portrait mode. Gently pinch the device at the midpoint of the left side, and squeeze it, applying very little force. If you can feel motion there and not in the same spot on the right side, you probably have the "screen lift" problem. Whether you can live with it (as I do) or prefer a return/exchange (as others have done) is entirely up to you.
Creaking while putting pressure on different portions of the unit may simply be the flex that is built into the design to keep it from snapping like a dry twig every time you pick it up,or it may be a loose back panel (especially if you've taken it off a few times, deforming the retaining clips in the process). If you can find a display model somewhere at a local store, try it out to see if it exhibits the same behavior. If it does not, you'll have to decide whether the defect is bad enough to you to warrant an exchange.
Putting the device in a decent-quality case will cure many ills, and prevent damage from many incidents. Nexus 7 cases can be had starting in the $10 range.