Well, and the thing is, you look at Kindle (I think) and Nook and Kobo and they all seem to follow the "dump everything into the same library and provide a few sorting options" philosophy.
That's great if you have a small library. Or if you only sideload a few books at a time and delete as you go. But as your on-device library grows, that method eventually that becomes HIGHLY unmanageable.
I have a library of 1,400+ books and I keep them on my Sony 950
all the time. You simply cannot support that with a big "bucket o' books" and a few sort options. The Sony collections are mandatory in order to use my device meaningfully. (Seriously, I can't even remember the titles of half the books, so the Search function is equally useless. Tags! TAGS, PEOPLE!
)
Somehow, Sony managed to get it right and the Calibre people filled the gap. (Also the PRS+ lets you browse by folders, if that's your thing.) But for reasons I can't understand, the newest and cheapest readers still don't support metadata meaningfully.
That, incidentally, is why I bought a $200+ PRS-950 the week the Nook2 came out.
And I really REALLY do not understand why B&N et al don't hire a few heavy users as consultants. Most of the people here would consult for "free" if they got a free Nook out of the deal. It's not rocket science.