This gives a side by side example of pixel fonts at their proper and improper sizes.
http://www.republicofcode.com/tutori...al/pixel_blue/
Image from the article:
The font on your nameplates is a proper multiple of the font's native size.
As a comparison, look at the font on your unitframes (the name, specifically) and the data text on your minimap. Each letter varies in width and the Visitor font is supposed to be even.
Also, if you're 100% sure you're only using sizes 10, 20 (whatever the proper size for the font is), etc... if an addon is scaled it might change the size of the font. You'll have to unscale the object or adjust the size of the font so it's the right size (ex - addon is at 0.8 scale your font might have to be 8 instead of 10).