I read that they were mostly assimilated, but the Bayeux tapestry shows that they used Viking-style longships including dragon-heads for example. Do you know of any other examples in their customs, language, weapons etc?
It's far from a comprehensive answer on the Norseness of the Normans in 1066 but I discussed the question of Norse language persisting amongst the Normans, over here. Some of my points there apply more generally too.