Serif versus sans-serif fonts
To begin, according to Wikipedia:
In typography, serifs are semi-structural details on the ends of some of the strokes that make up letters and symbols. A typeface that has serifs is called a serif typeface (or seriffed typeface). A typeface without serifs is called sans-serif, from the French sans, meaning “without”. Some typography sources refer to sans-serif typefaces as "grotesque" (in German "grotesk") or "Gothic", and serif types as "Roman."
The concept that "the simpler form of a letter the simpler its reading" was an obsession of beginning constructivism. It became something like a dogma, and is still followed by "modernistic" typographers....Ophthalmology has disclosed that the more the letters are differentiated from each other, the easier is the reading. Without going into comparisons and details, it should be realized that words consisting of only capital letters present the most difficult reading - because of their equal height, equal volume, and, with most, their equal width. When comparing serif letters with sans-serif, the latter provide an uneasy reading. The fashionable preference for sans-serif in text shows neither historical nor practical competence.
Ryan Newman, of the Interactive Visualization blog, says:
In choosing typefaces for dashboards, you will always want to use San-Serif fonts, that is fonts without the serif accents. Arial and Verdana are san-serif fonts, and enable an end user to read text on the computer screen much easier than serif fonts (example: times roman). Serif fonts are best applied in large bodies of printed text for readability. There is no value in using multiple fonts in a dashboard, so pick 1 san-serif font that works well for you.
If Information Dashboard Design is any indication of Stephen Few's opinion, he agrees with Ryan Newman. The text of the book appears to be in a serif font (except the headers and chapter titles), while every chart and dashboard example he created features a sans-serif font. Tufte, by the way, seems to publish the text of his books in serif, while his visualizations can be either type of font.
Garr Reynolds, a design and presentation expert, on the other hand, published Presentation Zen: Simple Ideas on Presentation Design and Delivery entirely in sans-serif. In fairness, sans-serif fonts are simpler, which is in the title of the book.
The U.S. State Department has banned Courier 12 in favor of Times New Roman 14 (both serif), except in the cases of telegrams, treaties, and documents drawn up for the President's signature, because "[Times New Roman 14] takes up almost exactly the same area on the page as Courier New 12, while offering a crisper, cleaner, more modern look".
Personally, I tend towards serif - especially Times New Roman - for most text and sans-serif - especially Arial - for visualizations in my own work, but I do like to pepper it with Comic Sans or Wingdings, just to jazz things up (kidding). There are no definite conclusions to be drawn, really. Draw your own based on trying to read what you created whilst squinting.