I've been thinking over this today, and yep, I still like it ;-) It reminds me that [the first time through](https://physics.meta.stackexchange.com/questions/304/what-should-our-site-look-like), there were a lot of suggestions about cute ways to work physics concepts and notation into the design, but I think we'll be better off with a design like this that just gets out of the way, so to speak.

Personally I'd be quite happy with the exact design you've posted screenshots of, but I do have a few speculative thoughts:

- The page footer seems insufficiently distinguished from the rest of the page. Maybe it's just me, but I think it would be nice to have some visual indication that the main content of the page has ended and that you're now looking at a generic footer. What about putting the same grid and gradient you use in the header, or perhaps a faded version of it, as a background for the footer?
- Same goes for the right sidebar; it seems insufficiently distinguished from the main content of the page, though more so on the question list than the individual question page. Of course I'm not suggesting using the grid/gradient background for the sidebar, but perhaps there's something subtle that could be done there, like giving it a faint left border, or a slightly off-white background color, or fading the text, or whatever tricks you have up your sleeve for this sort of thing ;-)
- Regarding the vertical alignment of the text of the site name and the page tabs on the right (questions, tags, etc.): when I look at it closely I do see that the baselines are aligned, but if I'm not focusing on that alignment specifically, it qualitatively seems just a little off. I'm wondering what it would look like if the names of those tabs were raised up by just a couple of pixels.
- The tags also seem to blend into the background a bit. What would you think about putting a thin border of a marginally darker shade on the left side of each tag?

Also, do we get a custom image on the 404 page? That's one place I think we could get away with having some cute physics joke.