I agree that the sound quality of my Sony 818 is significantly better, but I can't agree with the other comments. I think the interface of the Ipod is much more intuitive and there are more flexible options regarding playback, playlists on the fly etc.
I'm also a tad disappointed in the build of my Sony. When I first saw one in the shop on display, I assumed, rather like with mobile phones, it was a "dummy" model. I was therefore a bit surprised when I opened the box when mine arrived in the post! It has a rather light, plasticky, disposable feel to it. Certainly not a patch on my daughter's new Nano.
But I forgive all that for the sound!