It does look horrible on the 3.0 ROM.
I have tried it and it stretches the rosie launcher all the way across the bottom of the screen and the widgets aren't resized.
The widgets are the same size as in portrait mode and are on the left side of the screen and the bottom of them is cut off.
Plus, it scrunches your contacts photos if you are using the People widget and they stay that way after you go back to portrait mode.
I am a big fan of Landscape mode because I use a docking station at my desk so I would love to see it happen. Who knows, it may happen in the future