If I were psychic, I'd tell you exactly when format and DRM will cease to be a problem for eBook readers. I'm not psychic, so this post is more general. Here's the thing. Format and DRM issues come up as problems primarily with e-Ink e-Readers: Kindle, Nook, and so on. Which makes sense. These guys are proprietary devices, sold by their vendors--Amazon, Barnes & Noble, and so on--to make it easy for you to buy eBooks from them whenever you want to. They are also a convenient way for you to read eBooks, but that's a secondary purpose.
If you've installed Kindle for the PC or Nook for the PC on your laptop or the OverDrive App on your iPad, you've noticed that you can read stuff from Amazon, the Library, the Apple store, and Barnes & Noble on the same device. A different App for each, yes. But the same device.
So, I'm seeing the first crop of e-Ink e-Readers as transition devices. They helped us over that barrier separating pleasurable hard copy reading from pleasurable eBook reading. But they are already a little quaint and old fashioned. Not obsolete, but outmoded. When we all have that one device that convergence is leading us to, we won't need them. Format won't be an issue at all. DRM will do its best to keep us from ripping off the author, but it will seldom get in the way of our own reading pleasure. The flip side is that we may not 'own' any of these convenient-to-use books. We may simply have ongoing access to them. Is that enough? Maybe. We'll see.
DRM and format issues won't go away at some particular instant. They'll gradually lose importance as our portable devices get smarter and cheaper and as more and more of us have them. I'll lose interest in them when I can stretch my smart phone's screen to seven inches diagonally when I want to read and out to 15 inches when I want to do "computer" work.