Ok, I've seen a lot of speculation about how the memory loss caused by Sugar's powers could impact things, and while One Piece is a fictional setting, and not obliged to follow how the real world works, I want to clarify a few gross misconceptions people seem to have about memory.
First of all, forgetting events doesn't mean you forget what you learned from those events. People with amnesia don't, generally, forget how to speak or write a language, or forget facts and skills they have learned: they forget how and when they learned these things, because they don't remember their experiences.
Secondly, memory does not work like a camcorder. When you remember an event, your brain ties together a bunch of associations, and each time you recall that event, your brain reconstructs the memory from the associations. In fact, memories are highly unreliable, as your brain stores associations, but also edits your own memories, but then reassembles that into a coherent 'story' each time you recall it. And, in fact, it gets a lot worse than that. You see, your brain lies to you sometimes: experiments involving people whose corpus callosum (the bit that connects the two hemispheres of the brain) has been severed show that you can whisper an instruction in one ear of a person with a severed corpus callosum, and when they carry out the instruction, you can ask them from the other side why they performed the action, and they'll make up an explanation for their behaviour - and the side of the brain involved in making up the explanation will believe it. Their brain rationalized their behaviour that it had no explanation for by inventing an explanation, and insisting that explanation is correct.
If the memory loss from Sugar's power works anything like memory in the real world, the only memories they would lose completely would likely be memories that they associate specifically with Robin, and only Robin - a conversation they had with her, for example. They would still remember Enies Lobby, and nearly all of the events therein (they might be fuzzy on some parts, though), but their brains would have reassembled their remaining memories into a narrative they would all find convincing, even though an impartial observer might find some conspicuous holes if they probed; for example, your brain might convince itself of some invented reason why you needed the key to some kairoseki handcuffs, but if you relate the story to someone else, your explanation might not make much sense. That's not guaranteed, though: it might reassemble the memories so they remember needing the right key, but they don't remember it being for kairoseki handcuffs. In that case, though, if they got together and related the events of Enies Lobby, the crew might find that their memories of what happened and why were not the same from person to person.