I experienced a similar issue. Got my first iPhone 6 from the Apple store in Basel about 2 weeks ago. After 2 days the bottom left corner startet to give way just a little bit when pressing, along with some "click" noise. I returned it and got a new one, which after a few days showed a similar problem at the top left corner. I also returned that one and got a new phone from a german retailer. Same problam again, after a few days the top left corner, close to the volume buttons, startet to move just half a milimeter when pressing gently. Very frustrated, I wanted to return that phone today. Luckily I unboxed the "exchange" phone right in the store, because it showed exactly the same problem as my very first one (bottom left corner, but this time with an even loder click). The manager of the store tried to tell me that "all of the iPhone 6s of our staff have that" and basically told me that I am oversensitive. What he wanted me to believe was that this is some sort of "tolerance" to keep the screen moving a little and prevent the glass from scattering due to tension. Yeah right, it's not a bug it's a feature.
I ordered a new phone from Apple just a few minutes ago, and I can't wait to see which corner is loose thsi time. I'm starting to belive this is a general problem with teh new design. 4 phones, bought in 2 different stores in 2 different countries, that's no longer a coincidence to me.
Don't get me wrong, I rally am a big fan of Apple products and proud owner of more thatn one of their devices. But one of the reasons I pay that much money for a phone, is that I want to have a perfect constructed high end phone, which (to me) the new iPhone 6 does not seem te be.