Also, DNA kept in a dry, cold environment has an effectively infinite lifespan. Now, the interesting question becomes "what fraction of the the lifespan of the universe can I maintain my data with arbitrary accuracy?"
Next, existing technologies are more mature. They provide off-the-shelf products that integrate into a large ecosystem. So, DNA would have to provide some niche value that hard drives or flash drives don't.
Finally, with durable storage mechanisms, you don't really know how well they work until you deploy many instances of the mechanism for their lifetime; for DNA storage, that would be billions of cells (or more likely, passive storage containers) for decades or more.
So, I'll go with tapes, hard and flash drives and everybody else will too. MSFT made some claims about rolling out DNA_based storage in the decade-future, but they're blowing smoke.
1: http://onlinelibrary.wiley.com/doi/10.1002/anie.201411378/ab...
Showing you can store a tiny amount of data and then claiming you have a density higher than hard drives isn't just poor marketing, it's outright lying.
To show durability, you need to actually test things for the planned lifespan, or use intelligent mechanisms to test in a shorter lifespan. Then you can claim durability.