i have not used it, but it seems like most people complain that the battery life is not as stated, so that's an issue you might want to take note of.
and of course, the x-fi is very much different from the real deal (i.e. the sound card thingy)
if you're into sound quality, which i have a limited idea about; my advice is, don't delve too much into it. only the audiophiles are going to care a lot about sound quality. it is like how most people not into photography will tell you that P&S pictures not much difference from DSLR pictures mar.. that said, getting a good pair of earphones/headphones will generally help a lot with that.