[salmo]

I don't have data to back it up, but I've understood from typography gurus that sans-serif fonts are great for signs, short blurbs, etc. But for long (multi-paragraph) reads serif fonts reduce eye fatigue. I think blogs typically fit in that category.

[snazz]

This is true on paper. Sans serifs are more readable at small sizes on lower-pixel-density screens.

[mark-r]

The research showing that serifs aid in readability are based on printed samples, which are much higher resolution than most screens.