I'm looking forward to this.
I have 3 friends that have my login info and go on the account when I allow them to, we won't need to go through that trouble now.
I have friends that study/work/sleep all at different times and aren't playing games all the time, I can see myself playing their games while they are doing other things.
Along with that, all saves/files/items/achievements are on a steam-account basis. So my friend on CS:GO will have his own items/stats and etc.
Those 2 things sound very usefull for me and my friends in the future.
For the people complaining about sharing 1 game at a time... games would lose way too much money on SP games. I have so many games I beat and wont be playing anymore, I could just lend it out to anyone who wants to play them and they would never buy it.
I completely understand why they did it this way and I still foresee myself using this.. A LOT.