Where can I see how much storage I've used and what's left?

The dashboard's Account Overview shows hot and cold usage versus your allowance at a glance — something like "132.6 GB of 2,000 GB used." The file manager and cold storage headers repeat the same picture with percentage bars as you work. It's worth checking before you start a big upload rather than after, because discovering you're at 99% mid-upload of a wedding is not a fun place to be.