Imgur album here.
There are 4 screenshots in the album above: "Native" DT, "native" other forum (phpbb-based I think), "2x-zoom" DT, "2x-zoom" other forum. You can see that the phpbb-based one is OK in the sense that everything has correct relative sizes (but it is tiny because the resolution is huge), and then 2x-zoom brings it to the usable/normal size. DT's relative sizes are kinda wrong.
On my own website there were mismatches like these happening because I used a mix of "fixed" (e.g. px) and "relative" (e.g. '%' or 'em'). If everything was "fixed", then the site would look tiny in the native HiDPI (much like that phpbb-based forum) and zoom correctly; however I've converted everything to '%' and 'em', and now the site looks the same whether on normal resolution or HiDPI.
HiDPI (in my case 227 DPI) is not very well supported in general, but I managed to get my linux going somewhat OK (X has correct DPI set, xft as well, etc...). Webpages are quite a different matter. Some of them are OK, some are not. DT is not.
Finally: DT looks fine on my retina macbook; it only gets weird when I go into linux and use the native resolution in a browser.
EDIT: I've tested now that if I enforce 96dpi in the browser, things go back to "fine" in the sense that everything is uniformly small (and can be zoomed). However it would be probably nice if this hack wouldn't have to be applied
