Aggiungo questo estratto dalla documentazione di lettrine:
Important notice: the sizing works fine with fully scalable fonts (like the standard PostScript fonts), but might not work well with CM/EC fonts which have two limitations: only a limited number of sizes is available by default (precise adjustments are impossible), and the largest size (25pt or 35pt) is often too small. The CM fonts are now available in PostScript type1 format for free, to make them fully scalable, it is mandatory to add \usepackage{type1cm} in the preamble of your document. The EC fonts are also available in type1 format for free (hey are called cm-super), and adding \usepackage{type1ec} in the preamble will make them fully scalable too. So, if you want lettrine.sty to work properly with CM or EC fonts, you will need PostScript versions of these fonts and one of the packages type1cm.sty or type1ec.sty.
The newly released LM fonts, which should replace both CM and EC fonts sooner or later, are fully scalable, so, if you have them installed, you should use them instead of CM or EC fonts. \usepackage{lmodern} is the command to switch them on (add \usepackage[T1]{fontenc} when composing in one of the western languages other than English in order to get proper hyphenation).
Il passo in cui si afferma che i font latin modern dovrebbero presto o tardi sostituire sia i CM sia gli EC mi sembra notevole, per la nostra discussione.
Ciao,
L.