Great draw.
United should head into the Q/F (finally!) without too many problems, should settle the tie in the away game itself.
Milan are lucky to draw Atletico. They should be able to see them off but given Atletico are in top form atm there's a possibility of an upset. Allegri's credentials will be seriously tested if that happens. But Milan should see off Atletico.
Biggest losers are Arsenal and Man City. Wenger saw this coming at the final whistle of the Napoli game. Interesting tie, Bayern should be favorites but Arsenal have not lost outright in their recent ties against them (third time lucky?)
Barcelona vs City should be the top game. City's games against Barca have been friendlies. This should be another one :P.
Both teams will be tested. City can't be ruled out, why not; their manager has a better record against Barcelona and he's never had a better squad to face them. Should messi return with total fitness City will have a hard time. Interesting tie.
PSG, Chelsea, Madrid and Dortmund will get their Usual Q/F places.