You're assuming<p>A. You will always have internet access.<p>B. You will always have unlimited internet access.<p>C. You will always have very fast internet access.<p>D. Dropbox will always be online when you are.<p>I stopped using Dropbox 3 years ago for these and other reasons. Backup to a local external USB disk, and backup to an offsite file-server that you also control. You only need incremental backups, so your throughput is low.