Ligatures are missing :( Look at the IE5 screenshot. The second last line has the word "finibus" and notice how the "f" and the "i" seem to be combined together. That's a ligature. In contrast in the body text of the website I don't see any. The word "file" in the paragraph right above the screenshot is missing that ligature. Kerning is, well, also wrong. So wrong that I literally trouble reading the body text, but I…
Actually, IE5 didn't do automatic ligatures; what you see in "finibus" is simply an "f" glyph and an "i" glyph which are close enough that the dot of the "i" nestles into the top-right of the curve of the "f", and the serifs at the base run together... just like they do for the "in" and "ni" pairs following. (It was possible to render a real fi glyph, but only by using the Unicode presentation-form code point U+FB01;…
That's actually a really neat solution in the absence of explicitly defined ligatures... since there is no antialiasing, it only needs a little care when designing the font at the pixel level and choice of kerning and the result will be indistinguishable. fi is a very geometrically natural ligature though, i wonder if it doesn't work so well for others that are too dissimilar to their components.