From what I read, the latter. Like you said, overdoing it quickly makes a text look bad, and it also ruins the (presumably) carefully created kerning tables tha

From what I read, the latter. Like you said, overdoing it quickly makes a text look bad, and it also ruins the (presumably) carefully created kerning tables that are supplied by the font. I assume you have read Hàn Thế Thành's paper on microtypographic extensions to TeX (http://www.pragma-ade.com/pdftex/thesis.pdf http://www.pragma-ade.com/pdftex/thesis.pdf)?