Everything times 2
I know this will seem obvious, but when you have twins, everything is doubled. But there is a difference between knowing there will be two of everything and experiencing two of everything. I am constantly surprised by this 'two-ness'. We now have two high chairs set up for the two babies who are starting on solid food. (Not that full tummies is helping them with their sleeping much.) We make more beginning baby food than we ever had before and need more hands to feed them. And then there are two faces (and hands and heads and knees and...) to clean. But they really are twice as cute to watch and play with.
And while I'm on the subject of doubles, I never really thought about what two teething babies would look (and sound) like. J. asked me the other day if I thought two screaming babies could cause permanent hearing loss in parents.