I just updated from Lucid to Natty (thought it was going to be Maverick, but my About Ubuntu menu shows that it is Natty, which "was released in April 2011" - who knew the developers had mastered time travel?!)
In any case, the default date/time applet in my gnome panel is now displaying on two lines (date on top of time) instead of one line like it used to.
Any way to get it back on one line?
I've tried the instructions shown here, but it doesn't seem to make a difference.
You need to fix the core issues. Natty isn't released yet and only testers and the brave should be trying it out (although I'm sure many Ubuntu core people are already running it) it's going to have bugs. If you want a stable system, you should reinstall Ubuntu and go to Lucid or Maverick.
Now to the actual issue shown. It looks like the date time is on two lines simply because it has enough space to do so. The top bar is larger than it should be and you can see that from the other icons which have also grown to take more space.
If you go into System > Preferences > Appearance then you can see the options for changing the font size and icon sizes which can have this effect on your top bar.