I have 4 kids, 2 boys and 2 girls. And right now, due to our home set up (we have family living in our basement) the girls share a room AND the boys share a room. It certainly comes with it's challenges, but I don't think that it's a bad thing.
My boys have pretty much always shared, with the exception of about a year when we first moved into our home. For the most part, I think they will have a closer bond. The biggest challenge for us sometimes is bedtime. The boys are 2 years apart, they go to bed at the same time and on occasion I have to lay the hammer down (lol) because they are giggling, talking or bugging each other. I have been known to make one go to bed in my room, and I bring them back in when they are asleep, if they just won't settle. The girls are 4 years apart, and because my little one is only 5 months old (still figuring out sleep schedules), they don't usually go to bed at the same time. One typically goes down first, and then the other some time later.
Funnily enough, even when we "get back" the other two bedrooms in our house, the kids will still be sharing! The boys want to have a shared bedroom and a "man-cave", and the girls are going to share so that we can have an office space.