I'm the PM for a horoscopes app, and I much prefer to use relative dates (e.g. yesterday, today, tomorrow) instead of absolute ones (e.g. wednesday, thursday, friday).

The problem is that the app serves a worldwide audience, and I don't always know the locale of the user. By showing relative dates, everyone feels happy that they are seeing today's horoscope today. With absolute dates I'd get a lot complaints that they were seeing yesterday's horoscope for instance.