When presented with the idea that either Serif or Sans-Serif fonts might be more legible, you might think there was some credibility to the idea:

Back in 1998 when Times New Roman was still widely used on the web, my then boss made sure we always designed our web sites with Arial, as she hated the look of serif fonts on the web. Was it the case that sans serif fonts were more legible, or was it just a matter of taste?

As it turns out, there's a lot more to it.