Early this morning, Ubisoft left a twitter, plainly saying :

No we won’t add trophies in Assassin’s Creed PS3 but there will be in Assassin’s Creed 2 for sure.

So, there you have it. An absolute confirmation that the Assassins Creed won’t be getting trophies. However, the sequel, releasing later this year, will be getting the required trophy treatment.

Ubisoft’s Tweet