I installed Google Drive's "Backup and Sync" app for Mac yesterday, and within a couple of hours I get a mail from Dropbox saying - "We noticed that you haven't added any files recently. Save important PDFs, photos, and work docs to Dropbox to keep your files safe."

Is this just a coincidence or did they react to me installing Google Drive? Thing is I've never got this email from them before, so it made me suspicious!