Thanks for the replies so far.
We're a group of 9, so the 18% gratuity will automatically be added, so there won't be an awkward situation where we're looking cheap. I do have an issue with tips being added on automatically, as there are cases where poor service doesn't justify it, but we'll just have to make do.
I guess I'll plan on having it charged to the room/s and settle it with gift cards at check out.