Computer screens resolutions are getting better, leading the folks at useit.com to offer new guidelines for the best screen typography for online reading.
The old usability guideline for online typography was simple: use sans-serif typefaces. Because computer screens were not good enough to render serifs properly, attempting serif type at body-text sizes resulted in blurry letter shapes.
Unfortunately, the new guideline is not as clear-cut as the old one. Legibility research is inconclusive as to whether serif fonts are truly better than sans serif.
According to useit.com: “Almost all mainstream printed newspapers, magazines, and books use serif type, and thus people are more accustomed to reading long texts in this style. However, given the research data, the difference in reading speed between serif and sans serif is apparently quite small. Thus, there’s no strong usability guideline in favor of using one or the other, so you can make the choice based on other considerations — such as branding or the mood communicated by a particular typographical style.”