This is a defect.
I've had a few conversations with Nokia quality (including Mr. Elop, himself) about this issue.
You can see my other post (My Email to Stephen Elop and response!) for more details.
To those who are saying "no big deal," I understand. It's not a big deal in the long run. However, as a mechanical engineer, I'm concerned with quality, and I feel that Nokia should want to know about an issue like this (which they very much do).
The entire top portion of the chassis is loose. If you press on the top above the Nokia (fairly gently, actually), the chassis flexes. You can see it flexing. Eventually, the whole top flexes and it flexes when you pick it up by the sides. This is after about 3 days usage, no hits, drops, or shocks of any kind.
I'm on my third 920. This one has been perfect so far. Also, it doesn't get nearly as hot as the first two. I'm fairly convinced that the excessive heat (uncomfortable to hold) is related to the chassis issue. On top of the chassis issue, there's some kind of minor screen delamination going on around the earpiece. I had that on the first two, as well.
tl;dr
Nokia is aware of and concerned with this issue and is working on a response.