We just returned from OKW and BLT - did an online checkin for both and probably won't bother again.
At OKW, it was almost pointless... Our room keys were pre-printed, but the CM still needed to swipe our credit card - said the information is not downloaded from the check-in system to their system. Maybe saved some time printing room keys, but that was about it.
At BLT, our reservation was more complicated - we had two reservations that were linked (a waitlist came through). In this case, the credit card wasn't needed, BUT, we had to wait for the room keys to print for the entire linked stay.
Personally, I think the online check-in works best if you've got a very vanilla reservation with nothing 'different'. Otherwise, it probably gets in the way.
My two cents...