I do realize that the DRM books will only work on that specific Kindle. One good thing about Amazon is that any books I buy there stay available in their cloud for any Kindle I have or buy in the future (at least, as long as they stay in business and deign to keep it that way).
Just to be clear, I still think it's worth putting your DRM'd books into Calibre, since the management functions will still work, and I think Calibre is the best way to manage an e-book collection.
I've been wondering though, what about other vendors-- B&N, Apple, etc.-- are books you buy from them able to be re-downloaded to a new device in the future, say if your old ipad or nook dies and you buy a new one? And what if you buy a DRM'd book from an independent vendor? How does that work? (I don't know and that's one reason I've just gone with amazon if I buy a DRM book since I know how it works with them).
I think most vendors use Adobe DRM on ePubs, and as long as your device/application is registered to your Adobe Digital Editions (ADE) account, you can move between devices. So, if you bought a new device, you'd be fine as long as you were able to register it to ADE. The only form of DRM I've seen from independent vendors doesn't actually prevent it being copied - instead, they put some sort of identifier on the file, so that they can trace where copies came from.
From what I can tell, Apple is an exception, and books bought from Apple will only work on Apple devices.
Russell