There is definitely a seperate skill to downclimbing that isn't evident during an ascent.
My friends and I just summited Whitney via the Mountaineer's Route. It also just happened to be our first attempt on Whitney.
From my standpoint the way down was much much harder than the way up. I didn't have much a problem with the last 400 ft up or down and was surprised how little I was bothered by the exposure. However I hated going down the chute. Perhaps it was the route we took but I felt like I was just skiing on skree the entire time and I couldn't keep my footing. For me this was the scariest part of the trip.
Additionally, I was quite scared of the eledges on the way home until I actually got there. We were behind a group who knew the ledges really well and they took us through a short cut that avoids one of the most exposed sections of the route. That said... it was still pretty exposed and one member of our group had a hard time with it.
In terms of preparing... not sure what to say. I can really only share my experience as I am not an expert myself.
