I disagree. A local tape NAS is also not a good backup, (god forbid) your house can burn down. A remote service like Backblaze is also not a good backup, they c

I disagree. A local tape NAS is also not a good backup, (god forbid) your house can burn down. A remote service like Backblaze is also not a good backup, they could go bankrupt or a software error could corrupt all your backups. A good backup policy uses a mixture of onsite and offsite, and Dropbox can be a (convenient) part of that. E.g., I store (non-sensitive) files in Dropbox, which gives me a certain period of undelete possibilities. My Dropbox folder is backed up on a local time machine backup. Critical parts of my Dropbox are also backed up using tarsnap, etc. A good backup policy diversifies, and Dropbox can be part of that.