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)