You never realise this in India but when you are in the US there is a huge cultural impact of the term 'TGIF' (Thank God it's Friday). The whole system is geared towards the weekend being the most looked forward to of all days. And if there is a long weekend then you will find most people flying out to various destinations arranging to meet loved ones and having a blast while doing so.
After a really gruelling work week a Friday means that you will see most people smiling at you irrespective of who you may be. Even during my grad days in Rolla I have seen people just smiling and generally happy on Fridays. As it is the US doesn't really have an extensive list of holidays like India does, so the common public makes the most of those precious ones that do come by.
It starts out with Friday evening, people going back from work and planning to headout to some happening joint which would be the buzz around town, partying till the wee hours of Saturday morning and then heading back home for some rest. Saturday nights (SN) are also pretty much similar to the Friday night (FN) culture. However most people who have already partied on a FN try to avoid another round on SN. The people who do end up clubbing on a SN are either the die hard party goers or those guys who missed out on the previous FN. Most people though end up spending their time at a fancy restaurant or just relaxing at home with buddies. (Mind you, this doesn't prevent them from getting stoned though.)
In India nightlife usually means SN as most people work on a Saturday as well. However recently DUI has become a major issue in most metros and most people are having some sort of designated driver while traveling in groups. Also most regular people aren't really the partying types and end up just relaxing at home and watching a movie or something similar. Sundays are also pretty much relaxed with just some friends meeting up and going out for lunch etc.
In the US the Sunday is usually reserved for recovering from the hangovers one may have based on their SN experience. (I have become a veteran is this issue now...lol). Also people finish up what they may have to leave out during the coming work week (shopping for essentials, laundry, paying the bills etc.)
Bottomline: The US motto " Work Hard, Party Harder"