...on my Steam account.
I have a total of 328 games (well,actually they aren't all games,because I counted in all DLC,every dlc has a single game,betas and free games for all on Steam).
I've obtained 71 games for free (Steam promotions like Portal 1 or F2P games like TF2, or by a gift from someone).
I bought 134 games at 75% discount or more (but some games at 75% where in a bundle,like Doom and Quake games).
I received 115 games from bundle without beating the average.
I bought at full price 8 games (well,they aren't really full price. Ie when I bought Alan Wake it was at 20% discount,when I taken American Nightmare I purchased it with a 25% discount.Also,some games like The Basement Collection has a 30% discount,Home too has a discount and a very low price).

Considering a media of 8 hours to complete each game, I must spend 2624 hours, or 110 full days to finish every games.
So,probably I will never clean my Steam Backlog.And there are also about 30 games from Gog :\

Of the 328 games, you haven't finished any yet? Surely you must've finished a number of them. Plus some, like TF2 can't really be 'finished' AFAIK. And is there a site or Steam tool that helped you do these calculations?

Yeah I play games sometimes, too.

Yeah,I've finished some games,of course.
I calculated 8 hours for each game because some games require me 20 hours,other 4-5 hours,other only a few hours or minutes (like Windowsill).
I made the calculation all by myself :)

Damn straight. Better get used to it. ;)