That you won't necessarily have to endure several weeks of eyewatering, toecurling, nippleshearing hell before things start to come easily. If you're well prepared and have informed yourself before baby arrives (you're on MN, so a good start!) then chances are you'll get through the first few awkward/uncomfortable days without too much trouble. I'm on week 5 and although I still have the odd wibble it's been nowhere near as bad as I had been preparing myself for.
That your baby will make it quite clear from an early age that when he/she is unhappy nothing in the world compares to a boob for comfort. To this end, it's worth making the effort to give Dad a role (in our house he does the burping and bathing, and often the putting-down-to-sleep), because there's nothing a (my) bloke hates more than feeling helpless, and nothing makes a (my) bloke feel helpless more than a screaming baby who won't settle for anything less than mum's milk.
That (and you will work this out for yourself very quickly) before every feed you should assimilate several cushions (including a v-shaped one, try googling Dunelm Mill for much cheapness), every remote control you can find, a drink (v important) and biscuits (chocolate are best but Hobnobs a respectable second), a muslin cloth and ideally a servant of some sort in case you forget any of the above.
That babies can be very sleepy for the first week or two - A)don't be misled, they won't necessarily always be this quiet! and B)it's ok to strip them down/change their nappy midway through a feed in order to wake them up a bit. Also, don't get too tied up with hindmilk/foremilk when your milk comes in around day 4 - feed from both breasts at each feed for your own comfort, if only for a few days.
I wholeheartedly second the advice not to have visitors on day 4 - I had to endure 11 people hovering around me in my living room while I tried to stem the tears and latch on an increasingly frustrated baby to my enormous football-shaped boobs. Let them come before and after, but NOT ON DAY 4!
That it's the best thing in the world when it works. Even when they're a few days old and they don't do anything, they still look up and wrinkle their nose at you when they latch on and it makes you just melt!