The headlights are more vertical on the Audi and the open mouth look on the up!'s lower fascia is truncated by Audi's trademark split grille. The C-pillar is more triangular than the up! and the taillamps look like they were ripped from an A4 and stretched vertically.
Auto Express is reporting that an Audi version of the up! will be available in 2012. If that's true, it's unlikely we'll see the micro-Audi in the States in '12 anyway. We colonials aren't usually up (rimshot) for spending a big premium for a really small car that isn't named MINI.
[Source: Auto Express]