I have about 130 commercial ebooks on my Kindle, plus maybe 20 or so on the Kobo, and 3-400 freebies across the two. I have 25 unread paperbacks just in the "overflow parking" on the floor near my feet, and many more spread around elsewhere.
Most of the ebooks, I probably wouldn't put in my TBR. A lot of the freebies I don't really care if I never read, and many of the commercial books were just random impulses from various sales and daily deals. I don't have a proper TBR, and I'm slightly afraid of making one given that I'm always pursuing some kind of idiotic whim. Not long ago I collected all of the Hugo winners I hadn't read. I still have 13 to read. Currently I seem to be chasing golden age crime, particularly the four "queens of crime". I bought seven paperbacks at the weekend from charity and second-hand shops; five Agatha Christies and two Margery Allinghams. I think it's mainly about having an excuse to track things down, and find the best deals.
It's all about giving me a choice when I finish something, really. There are probably less than fifty that I really want to read, but many more that I kind of want to read and might go for if the mood takes me. Many of the books I most want just languish on my Wish List because of agency pricing.