On February 26th, Kindle customers will lose the ability to download eBook purchases directly to their PC. If you want to switch to a rival eReader brand in the future, I suggest that you use the soon-to-be discontinued "Download and Transfer via USB" feature to archive your Kindle library.
I love Calibre. I've recently broken my E-Reader (Tolino) but all my books are backed up on Calibre so the only loss is the hardware (still sad but not as annoying)
It’ll break saving books you bought from Amazon, but you’ll still be able to send books you got from other places to it from Calibre. Fortunately barely any of my ebooks on my kindle are from Amazon (though my next ereader isn’t going to be a kindle, that’s for sure).