Rasperry I felt a bit of sadness for what might have been when I found out I was expecting a boy during my first pregnancy. I might have felt the same if it was a girl too though - it could just be the fact that you can only have one or the other, whatever the result is you've "lost" one of options so it's normal to feel disappointed rather than overjoyed! We build ourselves up to finding out the gender but at the end of the day you don't gain something new when you find out, you actually lose a world of possibility.
It helps to search Mumsnet for threads about how lovely boys are. I think there are a few. I'm not normally into gender stereotyping but I think at the time it did help reading about how boys love their mummies and are very cuddly, whereas sometimes girls can be the opposite 
Also, that stuff did come true for me
I am now very happy to have a son and wouldn't mind if the second one is another boy too! My 2 year old boy is so cuddly, he gives me kisses and says "mummy I love you loads loads LOADS!" and he is usually not boisterous or noisy like the horrid stereotypes of boys. He calls me "my lovely" and always says sorry and gives me a kiss if he thinks he's done something wrong or hurt me by accident. He always wants to sit next to little girls and give them feathers and acorns and sticks etc at a woodland toddler group we go to, but they always push him away!
In my personal experience I have found the boy babies and toddlers we know are less whiny and tantrummy than the girls.
When it comes to teenagers, teenage boys can be "mummy's boys" and can sometimes be more chilled out than teenage girls too. I know my teenage brother was a lot more chilled out than I was as at that age. If he got told off he'd just go and sulk in his room for an hour or so, and then emerge as if nothing had happened. Whereas if I got told off, I would have a big hissy fit and I'd perpetuate arguments with my mum all evening. My teenage brother was also a lot more helpful around the house than I was!
(Not saying girls are awful, just wanted to shine a positive light on boys for those feeling a bit of disappointment about their gender result!)