I wanted to find out after a horrible 1st trimester. Throwing up constantly, insomnia, nausea - I hated being pg, and finding out the gender half way through really perked me up! Plus I was finding out about the kidney function, heart anatomy, leg length etc - why not the gender too?
With DS, I was told at a 17 week scan (was in the states so scanned frequently!) that he was almost definitely a girl. DH and I were so sure he was a boy, we didn't believe the sonographer. then at the anomaly scan, we all saw the willy VERY clearly, and knew he was a boy for sure! I did cry for about 30 seconds after we found out - not because I didn't want a boy, but because I had these 2 dreams - one girl, one boy - and knowing that one dream was effectively over was a tiny bit emotional. Also I needed to pee so much that I was on the verge of tears throughout the scan. 
with this pg, we wanted to know again, and have had 3 scans (due to baby position) for the anomaly scan, and at each one have been told 99% sure it's a girl. Or a winkle free boy... Again, I did cry when I found out, but haven't slept for bloody ages, so was/am crying at everything! :o the pregnancy hasn't been so different, and I had no gut instinct this time, so it was very bizarre to find out baby is a girl! Sadly DH had to work so couldn't be there when I found out, but he is thrilled to bits to have a daughter on the way!
I love knowing now, and giving my bump a name, and telling DS he's got a baby sister. We haven't told anyone else the name, but with DS and this one, love referring to baby by the name they will have when they are born.
I get that some folk don't want to know, and like the surprise, but hate the 'ooh, you've spoiled the surprise' shit I got from some people. IMO the actual baby is a pretty big surprise, no matter what is between their legs - so knowing DS was male was great, but we had NO idea what he'd look like, what his personality would be like (which is probably for the best, as he is currently very busy being a 2 year old and thus ghastly), didn't know how big he'd be, or how much hair he'd have, or when he would smile for the first time, or laugh, or sit up, or walk etc etc. Those surprises have been wonderful, and knowing what was between his legs before he was born has made no difference to my enjoyment of getting to know my baby!