We did online check-in in June at OKW. The room key printer was temporarily down, but came back online while we were waiting at the counter...some problem in the back office took the key encoder offline, so our keys were not in our packet, yet.
Our assigned room also wasn't ready, so they switched up to another room...so in our experience it didn't save any time. However, one advantage, for those that are concerned about the posts that occasionally appear about Credit Card info security at the front desk...the online system places your credit card number into the system, so the desk personnel do not need to swipe your card. And the desk personnel do not see our full CC number on the screen.
From that stand point, online check-in may be a good thing, and I'll try it again for our December trip.