If people are looking for a very nice UI but don't want iPods than there is really only one option. You have to get something from iRiver, either the AK100 or the AK120. Expensive stuff, but the UI will be a lot better.
On a personal note I don't mind the X3 UI at all. I think it works just fine and is good enough for me. The X5 looks to have improved UI, so that might be worth the wait for those of you who want a nicer UI.
I was going to ask what the difference is between the X3 and X5.
Why not just improve the X3's UI and put out a downloadable update?