Wow. What a bunch of naysayers.
My idea was this: I find it annoying that I have to menu all over the place to find the tuner mode (I don't really like using the remote), and then I have to play with the tuner in a different manner than the player. Tony suggested having a similar UI for the tuner. My thought was that it would make a lot more sense to just go ahead and have the ability to put tuner presets in with the mp3 files. (I realize I'm just reiterating. Wait for it.)
The problems you all list stem from the fact that you're thinking about the tuner presets as if they were tunes. I'm just suggesting that there doesn't need to be a separate more that you have to go to. In other words, to make my idea fit with the current UI, when you select a tuner preset from the Playlists menu, it would automatically switch to tuner mode and change the station to the one selected. But instead of changing the ``default'' menu item, it would still contain the same things it did before, mp3 playlists and tuner presets. If you wanted to listen to another radio station, then you could select another preset from the playlists menu or you could use the left and right button or whatever to tune as you would now. But if you selected an mp3 or mp3 playlist from the ``Playlists'' menu, it would automatically switch back to player mode and start playing it.
The major problem would be with including a tuner preset in a playlist, since there would be no way for it to end to go to the next song. I would suggest that that doesn't really make sense and should be disallowed. Another way would be to be able to define a length of time that it should play. (That would be more versatile, since it could possibly be useful to someone somewhere, and the rest of us could just set that timer to infinity and make sure not to place tuner presets in mp3 playlists.) (Actually, now that I think of it, in that paradigm you could set a default timer length in the playlist definition, and a playlist of radio stations could serve as a scan function. That way you could have a rock scanner, a jazz scanner, a country scanner, etc.)
An alternate suggestion that's very similar would be to have a ``Playlists'' menu as we have now and a ``Radio'' menu next to it, both of which would be available all the time, probably with the default being the one that's currently active. Otherwise, it would work the same as I suggested above, but the mp3s and tuner presets would be segregated. And you could long press on the ``Playlists'' or ``Radio'' menu items to just switch to that mode, if you wanted, for some reason.
My whole thought is that there's no reason for such an advanced system to force you to switch to a particular mode. It should be able to figure it out on its own.