I've had my 505 for 15mths now and prefer it to pbooks. It's easier to hold and I don't end up breaking the spine so I can read the bits near the margin!! I still read pbooks though, if the book I want isn't available at a reasonable price (cue the threads on geographical restrictions!) I'll get it from my local library. I also still use paper for non-fiction, mainly history. This is because the choice in history ebooks is very poor and I'd be constantly trying to flick back and forth for maps/diagrams etc - not good on a 6" ereader. Having said that, if the book choices improved I'd probably consider getting an 8/10" reader so I could stay digital.
One of the downsides of an ereader though, is the size of my 'To be Read' list! I used to have about 3 books queued to read at any one time but now it's more like 100!!!