'Probably' may be putting it too strongly, but I do definitely buy yarn without a definite purpose, knowing that I already have more yarn than I will reasonably expect to knit in the medium-term. I don't think I've yet hit 'Stash Exceeding Life Expectancy' but I know a lot of people who have. It doesn't stop them buying more.

I think I probably have fewer books in a TBR pile because of the kindle, though I know I have done a lot more impulse buying at midnight and have consequently done a lot less re-reading than I used to, so I do have a lot more books than I otherwise would.