Mac mini + pivot = screen getting blurry

OS X relies heavily on sub-pixel antialiasing to make text on the screen look good at all sizes. It also makes assumptions about the order of the sub-pixels and assumes left-to-right R,G,B when "best for Flat Panel" is selected as the font smoothing choice in System Preferences/Appearances. When you pivot your screen 90 degrees, the subpixel ordering suddenly becomes a stack of R,G,B (or B,G,R depending on which way you rotate) and suddenly font smoothing is very broken.

You can experiment with the various choices for font smoothing in the Appearances section of System Prefs and see if one of the other settings pleases you more. Good luck.

You are correct about SwitchRes X. It won't fix the type of issue you are experiencing.

In System Prefs/Appearance, try setting font smoothing to "Standard-best for CRT." I noticed that the anti-aliasing becomes gray scale anti-aliasing in that case. And gray scale anti-aliasing won't have any dependency on the ordering or orientation of the R,G,B sub-pixels.

Sorry if that sounds like a bunch of gibberish. Just try setting to the CRT setting and I think you will be happier with fonts on your pivoted screen.

By the way, if you have any interest in a close up view of color sub-pixel font anti-aliasing, you can open the DigitalColor Meter in the Applications/Utilities folder and use it as a digital magnifying glass to see what a character looks like under extreme magnification. Just pass the mouse cursor over some text and you will see the color fringes which are used to make the text look smoother.