it depends on the person.
i function best on 7. more than 8 makes me groggy all day and less than six makes me edgy and short tempered.
12? 10? even 8 Hours of sleep? ahh those were the days before kids 
I couldnt imagine getting so much sleep.The only free time i get during the day is when the wife and kid are asleep at 9pm and im usually up to 12-12:30am and up again at 6am.
Thats plenty of sleep for me.I should get more sleep on weekends but i stay up until atleast 2am.
Get your sleep while u can if u dont have kids,kiss it goodbye when your girl pushes one out.