I've not been satisfied with any dedicated reader devices I've owned, specifically the Sony PRS-505 and Kindle 2. I have been quite satisfied reading on PDAs and smartphones over the years though.
I think the e-ink readers just cost vastly too much money for the user experience on offer. Long battery life and a bistable screen is ... well it's interesting at least. But it's not worth the price of a full on PDA or whatever else you can get for $260+. I know they have their fans, even
because of how little they do. And that's fine. Dedicated devices have their place. But these devices also suffer more important problems such as awful UI design, painfully slow refresh rates, even for just basic navigation. They often render documents poorly and very rarely get updated to fix such problems. Just consider the Sony Readers and their ePub "support." Or the experience of reading technical PDFs on a very slow screen.
So while I still kinda think those readers are cool in certain ways, I definitely count myself dissatisfied with them. For what it's worth, I thought the display of the PRS-505 with an LRX book was really nice looking

I was never very happy with the K2 though as the screen suffered nasty ghosting and had worse contrast than the Sony, for whatever reason (whether fonts, or backdrop color, or the illusion from the white border, I don't know or care).
Luckily there are some hopeful new screen technologies up and coming, so maybe paper-like reading experiences will be coupled with better user experiences in the next few years.