Feasible font size on the Retina MacBook Pro I'm interested in the amount of text that can be fit into for example code editor windows such that it is still comfortably readable to someone with good vision (i.e. not needing glasses or using glasses that are well adjusted).

The new sharpness in this display is a great thing and one of the benefits is incredibly sharp text rendering. I've seen that on one of these new MacBook Pros.
However, having very good eyes myself, I was wondering how small one could set the font size in an editor. I quickly tried this in TextEdit, simply loading some big text file and changing all the text to a font size of 4pt, which was too small to be comfortable, then 5pt which was already much better (remember, this equals the amount of pixels of a 10pt font size on a non-HiDPI setup).
This of course is not the way to go, since these font sizes stay with the document and would look just as small on any other display, even though it might not be one with enough resolution to show it in a readable way.
Now, code editor windows are another thing entirely. They don't store the font size, as the code is not something that is for print. Its just letters in a file and the font size is a preference in the editor and set up to accustom the user. So this would be an excellent way to really leverage the incredible resolution and just reduce the font size, in for example Xcode, to get a huge amount of lines of text out of the 15&quot; display.
I'm not talking about the 1920x1200 scaled resolution that Mac OS X offers, as I've seen that already, it looks ok, but still not really sharp. To achive this scaling the screen gets rendered at 1920x1200 HiDPI mode, equal to 3840x2400 pixels and then downscaled to 2880x1800 pixels, making it quite slow.

So, I'd like someone with the Retina MacBook Pro to take a screenshot of Xcode or Coda or any other Retina aware Editor that is focused on writing text or code that is not intended as Rich Text. And to do so like I imagined, reducing the font size for the main text/code editing component. Be sure to also show enough text to sufficiently fill it up with text, in order to be able to judge the gain.
In Xcode you can do this like follows:

Open Xcode
Go to Preferences --&gt; Fonts
Duplicate &quot;Default&quot; theme
Change all the Source Editor font options (you can use Cmd+A) on the right to Menlo 6pt or 7pt.

Additionally I'd also like a screenshot of the same Application with normal font sizes but using the full 2880x1800 resolution. You can turn that on using SetResX from http://www.reddit.com/r/apple/comments/vi9yf/set_your_retina_macbook_pros_resolution_to/
Post full sized screenshots, please.
It is impossible to deliver an "answer" to this question. You are asking for something that is purely opinion-based. I have friends who use super small fonts and it's very comfortable for them. I also have friends who use larger fonts, and that works best for them. I personally use a variety of font sizes depending on what Mac I am on and what App I'm using. Your best best is to work with whatever font size suits you, despite what anybody else tells you.

There is no "one-size-fits-all" answer to your question.