It's generally accepted adults need 7-9 hours of sleep a night, with at least half being good quality deep sleep. Less here and there won't kill you right away, but it can add up over time and eventually catch up to you. You still won't die though. Too much has also been proven to be not beneficial.
And sleeping less than 7 during the week, and then sleeping til noon on the weekends doesn't count...
Mt Snow, VT - May 5, 2012 - Completed!
Gunstock, NH - June 1, 2013 - Completed!
...i remain, he who remains to be...