Good E Reader is reporting that Adobe is updating their digital rights management programs this July, meaning a lot of older ebook readers won't be able to read new books come this summer.
Here's a video explaining what this means (or go to their article if you'd prefer to read it).
I'll also point out that someone from Adobe commented on the article/video stating that some of the information is wrong - there won't be an 'always connected to the internet' feature and older books will still work with their devices, but new books won't.
My position is that if I'm buying something, I should own it and be able to read it on whatever device I choose. It's one reason I haven't been buying many ebooks (beyond SF bundles and kickstarter books that come DRM free). I'd love to buy more ebooks, but not if I'm crippled by technology so that I can't share my books over all the devices I own.
You can find more information about this at The Digital Reader (which also mentions the July deadline for stores to upgrade has been softened)