Let me just say this: my dad used his belt on me once when I was 7-8...that was the one and only time I ever needed to be corrected by him, but both my brother and I were spanked by our mom several times (him more than me).
My brother didn't even know who dad was until he was almost 6 (I'm 7 years younger than he is so I knew my dad from the beginning; huge difference). My bro was practically spanked nightly by dad from the time he was 6-7 to 16. Had no effect because (a) my bro was psychotic (b) he wasn't spanked when he was younger so he didn't fear authority. My bro has also been in and out of jail and almost went to prison before he snapped out of his criminal life at 18-19.
Also, my brother is Pinocchio (figure of speech) so that didn't help. Finally at age 30 he's started to become a decent person, in fact he just went through a very humbling experience which I believe has helped a lot.
My brother has three kids; 9, 10 and 11. The ten year old is a girl, the other two are boys. All three were spanked by him from a very young age...all three of them are the best behaved children their age. I cannot exaggerate how much control they're under...in fact, they look around at other kids their age in boyscouts/girlscouts and see how wild they are and literally tell us (me included) that there's something wrong. These three are also extremely intelligent (intelligence does run in the family, but this is abnormal).
Keep in mind that my brother doesn't spank them anymore, he just asks them if they want a spanking and that's the end of it since they know what it's like. None of these kids are anything like their father when he was their age, so genes aren't a factor, only the fact that they were spanked.
Conclusion: don't spank your kids, you end up with horrible children that don't grow up till they're 30. Spank your kids, and you have adults at 10.