The big problem with digital storage is longevity. Will archaeologists in 2000 years be able to decipher our culture?
This
is a serious concern. Vint Cerf, one of the "grandfathers" of the Internet, was just saying this recently in some news articles. He advises people to print things out, but this is simply impractical for all but a tiny fraction of your data.
A major problem especially with e-books is DRM, which I call "digital restrictions management". The file formats are difficult to read
by design, and you can't use your own tools to read them. I generally avoid e-books for just this reason, though I do patronize a few enlightened publishers like O'Reilly that eschew DRM in favor of open, standard formats (e.g., pdf) for which there's a lot of software support.
Another, more general problem is physical storage. I do have some old tapes and disks that I'd like to read someday, mostly for nostalgia, but I'd need to find a working drive first. This problem may be easing somewhat now that we no longer have media per se but media encapsulated with electronics that presents a standardized electrical interface, e.g., USB, SD or SATA. Even then there can be problems as old interfaces (e.g., PATA, Firewire, compact flash) are phased out.
What has generally saved me so far is periodically replacement of my hard drives as storage capacity rapidly increases. It's been easy each time to just copy everything from the old drives to a small part of my new drives and leave it there. (As my former boss and I once agreed, the best way to preserve old data is to "keep it spinning", i.e., online somewhere on devices you're still using and maintaining. Preferably with internal redundancy such as RAID). Interface changes (e.g., from PATA to SATA) are fairly easy to handle when the computer you're using at the time supports both. It gets a lot harder if you wait until after you've replaced your computer a few times and the old interfaces are no longer available.
But increases in hard drive storage capacity seem to be slowing down, so there's less incentive to periodically swap out my hard drives for bigger ones. If I want more room, I'll have to buy more drives and find room for them. I currently have four 4 TB drives in a RAID-1 configuration, and the array is currently 86% full. So it's either 1) find a new box with room for additional drives or 2) put some old drives on a shelf and risk not being able to read them in the future.