I have at least 10+ years' worth built up, and growing, but they'll be welcome when I retire. I'll have less disposal income, and a great stash bought on sale. I've done the same with art supply sales.
I bought my first ebook for a palm pilot in 1999 - but until a few years ago, only bought what I intended to read immediately ( though sometimes a full series). Then I met Alf, switched from Sony to a Kindle and discovered Amazon sales from 'the ebook addicts support thread'
. Excessive maybe, but better for me than hamburgers, and I don't buy stuff unless I'm pretty sure I'll enjoy them.