I have a rotatable display which I tip up so that I can fit more code on the screen.
However any text on the screen looks just the slightest bit less sharp on the rotated display. Can anyone tell me why this is, or better yet, how to 'fix' it?
That's probably to do with the ClearType settings.
ClearType uses subpixel antialiasing to smooth the edges of fonts. When you rotate the display the groups of red green and blue pixels will be in a different pattern (rotated through 90 degrees) but the operating system probably doesn't know about that.
http://en.wikipedia.org/wiki/Subpixel_rendering tells you all about subpixel antialiasing
One thing that could be a problem here could be due to the fact that the way due to how TFT monitors are made gives them a very limited range of viewing angles, typically they are optimized for viewing horizontally and look distorted when viewed from above or below.
From this Wikipedia article on TFT LCD monitors manufacture:
The "less sharp" impression could be due to Cleartype as others have mentioned, but could also be due to your monitor having a vertical viewing angle that is very poor. This vertical viewing angle would become a horizontal viewing angle when the TFT is rotated. What this would mean is that your eyes would be seeing two different sets of colours and your mind is blurring them as it merges them together.
I would expect this to have gotten better in the last few years as manufacturing processes have improved.
This is probably caused by ClearType.
You may either :