I'd like to report that the removal process went pretty smoothly. The only negative consequence was some slight discoloration on the door where the adhesive strips had been for so long.
We decided to hang our "whiteboard" at our new house because it's so useful to have a centralized place to record family-related things. We opted for the kitchen this time. Right now, we've been using to record our meals for the week (have you been using Meals for a Year, the free meal planning site we created?). I also write notes to the babysitter and include a packet of information about Henry's schedule (secured within one of those plastic sheet protectors).
If I erase the marker in a timely fashion, it comes off very easily. If I let the market sit for weeks and weeks, then I have to break out the nail polish remover to get it really clean, which I don't mind. Shower board is definitely an inexpensive option for large whiteboards! You could even build a frame around it, like John and Sherry did at Young House Love.