I think it will be a little while before you're nicely profitable, but I'd say it will come. Backups are just the worst thing ever. Getting the data to unreliable tape drives, rotating the tapes, dealing with finite capacity physical hardware, making sure that it's secure (both from people stealing the data and disaster happening to the data). It's a nightmare and one that I'm happy to replace with Tarsnap.

With Tarsnap, I can simply run a cron that creates a backup with the date in the name and I'm done. I never have to eliminate old versions since they all take the storage space of an incremental. I never have to worry about where we're storing the tapes (a crappy basement a block from our main building shudder). I never have to worry about people getting past the little security in the building. Most importantly, I don't need to do anything. The cron does it. I don't have to monitor tape capacity, constantly test whether the tapes are any good, deal with incrementals vs. full backups, etc.

There's no longer any excuse for having poor backups. Tarsnap allows you to do full backups as often as you want while only using the space of incremental. It's paranoid secure and replicated on S3.

Congratulations! You deserve for this service to become the premier backup solution for many IT departments.