One thing that regularly strikes me when I look at web comics is how often the lettering lets it down, not because the lettering is bad if taken on its own, but that it often jars with the artwork style.
Many strips have a beautiful, organic, hand-drawn look to them, but then the lettering looks way too formal because it's a font like Ariel or something similar. My feeling is that lettering should be done in a style which fits the style of the artwork and this often means that the artist has to resort to hand-lettering in order to acheive this.
OR...
Actually, I hate hand-lettering. So I decided that I would search for a font (or fonts) that complemented my art style. After a few experimentations and visits to various sites I found a great site which has a number of fonts that look like hand-lettering - www.blambot.com
One of the advantages of looking hard at your lettering in relation to the whole look of the strip is that it forces you to evaluate the style anyway and can often draw your attention to other areas you might want to change - line weight, panel proportion, timing, etc.
Anything that forces you to evaluate your work from time to time is a good thing in my view.