eReaders are great for reading entertainment books that you typically read only once and then move on to something else. But I wouldn't use a DRM'ed eBook for reference materials. Long term storage on electronic media is iffy in the first place, but when you add DRM to that, I think it becomes too risky a proposition to consider. It very well might not be there when you need it.

If you want something to keep, and refer back to in the future, possibly many times, a DRM'ed digital book is a very poor choice. But I had no qualms about buying a digital copy of The Hunger Games that was DRM'ed up the wazoo. I finished reading it. It was a fun read. But there are too many OTHER good books to read for me to worry about going back to read it again later. The digital copy I purchased has already served it's intended purpose. I would donate it to the local library if that were allowed. I can buy a hard copy of a book, read it, and then give it to the library so others can enjoy it. Not so with this new DRM nonsense. You can't donate or even lend (reasonably) a digital book, everybody has to buy their own copy. Greed has taken over in the publishing business.