”…reading online is much more difficult than reading on paper. Highly contrasting text and background colors make it easier. Black text on a white background or something similar is easiest to read. In general, dark colors are best for text, and cool, desaturated colors are best for backgrounds.”
Jakob Nielsen & Hoa Loranger: Prioritizing Web Usability (2006), s. 240

”The oldies continue to be goodies -- or rather, baddies -- in the list of design stupidities that irked users the most in 2005 […]. Bad fonts won the vote by a landslide, getting almost twice as many votes as the #2 mistake. About two-thirds of the voters complained about small font sizes or frozen font sizes; about one-third complained about low contrast between text and background.”
Jakob Nielsen: Top Ten Web Design Mistakes of 2005

”The vertical space in a text block is called leading, and it is the distance from one baseline of text to the next. Leading strongly affects the legibility of text blocks: too much leading makes it hard for the eye to locate the start of the next line, whereas too little leading confuses the lines of type, because the ascenders of one line get jumbled with the descenders of the line above. In plain HTML it is not possible to implement true leading, but CSS offers leading control (referred to as ‘line-height’ in CSS terminology). In print one general rule is to set the leading of text blocks at about 2 points above the size of the type. For example, 12-point type could be set with 14 points of leading. We suggest generous leading to compensate for longer line lengths and the lower resolution of the computer screen, for example, 12-point type with 14 to 16 points of leading.”
Patrick Lynch & Sarah Horton: Web Style Guide (2002-2005), s. 216

”Typefaces such as Georgia and Verdana were designed specifically for legibility on the computer screen; they have exaggerated x-heights and are very large compared to more traditional typefaces in the same point size. These fonts offer excellent legibility for web pages designed to be read directly from the screen.”
Patrick Lynch & Sarah Horton: Web Style Guide (2002-2005), s. 218