Windows Phone 7.8 was installed with Nokia Care Suite, making it a fresh install, no update.

Using it I noticed 3 differences so far:

• Of course the home screen with smaller / more tiles
• In WP 7.5 in the locked screen the music buttons where always visible, now only shortly after pressing the power button and the the disappear
• Nokia maps faces north instead of east

A challenge was making screenshots: http://qatsi.ath.cx/diverse/lumia_2013-01-26.html

All the points mentioned earlier still exist