My first post here, in 2009 shortly before my car arrived, wondered if I would miss the sounds too. In fact I also mentioned the possibility of artificial sounds as an option.
After more than 6 years, I can definitely say that I in no way miss the sounds. I find loud cars really annoying now. That's hard for an enthusiast to believe, because the sounds are so awesome. But if you think about it...noise is not a good thing by itself. The reason we like it is simply because we have associated the sound with power. If you drive an EV for a while, the associations will change. As xmetal noted, there are still noises, and you will come to love them. (Oh, how I love the subtle pod-racer sound my Roadster makes!)
I would guess the transition usually takes around 4-6 weeks - if you go full BEV. If you alternate driving an ICE, the noise association may never fully go away, though it won't be as strong.