That page mentions one thing I always look for in lettering, and which in my mind separates the men from the boys (if you'll pardon the expression): the use and abuse of serifs on the capital "I." Serifs are the little horizontal bars at the top and bottom. In proper hand lettering, the "I" should only have serifs when used as a standalone initial or the personal pronoun. An ordinary "I" in the middle of a word shouldn't. It's a subtle matter of emphasis and spacing. Here's an illustration borrowed from Blambot:
Now, the serif "I" thing has always been more a guideline than a rule (to quote the great Capt. Sparrow), and you can look through old comics and see where even the masters had their own opinions on the matter. For example, Walt Kelly had the quirk of also serifing any "I" that happened to start a sentence. Some used serifs on words like "I'm," "I'd," "I've," etc., and others didn't.
Still, seeing a serif "I" in the middle of a word makes me sad--not because two tiny lines matter much in themselves, but because it represents what I see as the slow decline and degradation of comics art in general. It's a small standard of craftsmanship that at one time every pro paid deliberate attention to. Now few do, or see any reason they should. There are many aspects of modern cartooning for which I'd say the same. Very few cartoonists working today would be fit to clean the nibs of an ordinary journeyman professional working 50 years ago, including me. ("Nibs? What's a nib?")
Lettering is an important and overlooked part of the art of comics. I consider my own lettering neat and adequate but not professional-grade, certainly not up to the standards of real practitioners in the field (go visit Todd Klein to get seriously schooled). Mine may have a certain handcrafted charm, and there's definitely something to be said for lettering that reflects the hand and personality of its maker. But as fewer and fewer people really understand or care how text works with pictures on a page, and any yahoo can buy or steal a nice-looking font and start typing away with the Caps Lock key on, it's a dying art.