Portable digital audio recorders

[XB-70 Valkyrie]

Recently I've seen some very slick pocket-sized portable digital recorders on the market. I was wondering whether these can give reasonable quality in playback, i.e., something better than your usual digital camcorder. I'd like to record myself playing the piano for one thing--not that I'm a great musician or anything, but I think it would be helpful for me to be able to hear what I sound like away from the piano. I'd also like to record nature sounds such as the beach, rivers, birds, etc.

Can I expect only a quality similar to the older microcassette recorders? What about if I bought a decent microphone to go with it? Any ideas?