Doug, your math is right, but as Tom said, most people aren't backing up 4TB of data.

What do you have that's taking up 4TB of data? If it's DVD/bluray rips, then that's also not the typical thing that most people are backing up. If it's all photos, then dang, you're a pretty prolific photographer Good for you!

Also as Tom said, very few of these backup companies are still offering unlimited storage. Some are, but they still bank on the assumption that most people are going to go with them because they think they'll need the unlimited space, but end up only using a few hundred GB at most, probably around 100GB on average (which might still be a little high).

Also figure that while your upload speed is typical (for the US at least, I don't know about Mexico), there are others with faster speeds. I have nearly 5Mbps, and it took me about a week for my initial upload of around 300GB. I do wish I had Bruno's 640Mbps connection, though Are you in Kansas City, Bruno?

After the initial backup, the differential backups are quick.

Online backup isn't feasible for everyone, but I'm a big fan of it because it works well for me.

I still think it's good to have a local backup as well...