I hope to get a demo unit soon and post a complete review. But in the meantime, reader Jon Skitch managed to snag an H4n and he sent me the following audio sample made using the recorder and a Rode NT1A microphone.
The noise floor appears to be much lower than on the Zoom H4, which means you get cleaner sounding recordings, at least with a high quality mic like the NT1A. While it's not an apples to apples comparison, you can check out a few recordings I've made with the Zoom H4 and an EV RE50b dynamic mic in my original Zoom H4 review and my Sony PCM-D50 review.
Update: Jon just sent in another recording. This time it's a musical performance and it sounds fantastic.