In the performance of Figaro I saw last week they all did little ornaments in the da capo sections of the arias. This has been standard for Handel for a few years, but for some reason no one before ever seemed to apply this performance practice to Mozart. No one gets too carried away about it, though.
Only Cecilia Bartoli seems to ornament for its true purpose, which is to show off how spectacularly fancy she can get. For this you must let yourself go.