You won't need to know the sex to prepare better. Unless, of course, you're going with traditional blue-boy pink-girl things. You can just pick a gender neutral theme, most newborn clothing comes in white anyway, and pick several names to choose from (which is a good idea in any case, because sometimes baby just doesn't turn out to look like the name you wanted). We were willing to find out at our last ultrasound, but the baby just plain ignored that the technician was there and didn't move. I think baby was asleep. So we're trying to prepare without knowing. It's not impossible.
It's a surprise whether you find out at the u/s or at the birth! And I think it makes the u/s extra special to find out. I did find out with my first, but I'm thinking of waiting with this one just for fun and to keep people guessing. Deep down, I know it's a boy though!
before I ever got pregnant, I thought I wouldn't want to know. But when I was actually carrying a baby, after so many miscarriages... yeah, I wanted to know. If I hadn't had my tubes removed, and if we ever were to have another baby, I'd probably not have any ultrasounds at all, or maybe just one to check the location of the placenta, seeing as how my first was delivered by cesarean, but not to find out whether baby is a boy or girl.