On FF in Windows, the fonts are extremely thin and difficult to read. I had to zoom in Nolen's blog four times to make it readable.

The main body of the text was extremely difficult to read. There's nothing wrong with the font itself, but the size is far too small and colour too faint. I had to turn off the font stylesheet to get to the text. It's too bad the same font as the sidebar section wasn't used throughout the body.

It's "possible to read" for me (FF on Debian), but it's not particularly "readable"... it seems to be using fonts that don't render very well for "traditional resolution" (~100dpi) displays, at an uncomfortably small size (maybe the author tests using a browser that tends to inflate text sizes?).