I've got the Sony ebook reader. I wouldn't pay the £200 odd quid for it but I lucked out and got one cheap on eBay (and paid for it out of the cheque from RFTP so it felt like it was free).
I love the thing. I commute about 2 hours each way every day so I get through a lot of books. Having the ebook reader means I don't have to carry round the massive book I'm reading as well as a spare one in case I finish the one I'm on.
I too have a phone which can handle pdfs etc. and a PSP which can work as an ebook reader but they're rubbish. The proper one has one of those screens which looks like printed paper. In fact I sometimes catch myself reaching up to turn the page!
I still like proper printed books, and often have one of those, in which case the ebook reader is there as my 'spare' ready for when I finish what I'm reading.