How to deal with Steam backlogs?

I wish my backlog was less than a hundred games still.

But seriously, I find it helps to actually track things, Backloggery is a good one and you can get a tool here to automatically scan for and add your games (though it doesn't do so well with DLC) to save some time.

Also sites like Astats and Metagamerscore can help. Stuff where you can actually see numbers go up and down can help push you towards playing stuff. There's one called Steamcompletionist that is good for games without achievements as well since you pick some games to beat and get a point for every minute spent playing it until you beat it or remove it. It also has a pie chart that shows your percentage of games played.

I have only played 32% of my games. :|

I too have a lot of games which I never player, most of them from humble bundle and the like.
Never felt the need to give the extras away as 100s of people already giveaway their extra games leaving the site spammed with them.

I know exactly how you feel...