Here is an example of his blog with better typography. I used 18px Georgia as the body text instead of 12px Arial. I used Droid Sans (a nice display font) for the blog title.
Body text, however, should be optimized for readability so your choices are more constrained. I don't think there is a huge difference in readability for serif vs. sans serif fonts for body copy. Ask a couple of designers and you'll get a couple of different opinions. Some will say that serif fonts are better because the serifs "lead the eye along". I'm not sure I buy that, but I do prefer serif fonts for body copy. But if you use a serif font, make sure it is big enough. At small sizes the serifs don't render well and get in the way of readability.
I've heard that Arial works better as a display font instead of a font for extended reading, which I tend to believe since it looks so much like Helvetica. If I choose a sans serif font for body copy, I choose Verdana which was specifically designed for the screen. But really, I don't think Arial is necessarily a bad font for body copy. I don't have any objective reason to say why you shouldn't use Arial.
Also, the header font and the body font should contrast, so if you have a serif header font it's usually good to have a sans serif body font and vice versa.
The general opinion used to be that serif was better for bodytext, and sans for title, and Arial is sans serif, but not one of the better ones.
Thing is it's mostly subjective, so YMMV.