While experimenting with the new unicodedata for version 5.1 (many 
thanks for it!) I discovered some strange behaviour of Idle with regard 
to a character not available in any font on my system, namely Latin 
capital letter sharp s - U+1E9E.
Cf. the following sessions:

Python 3.0rc2 (r30rc2:67141, Nov  7 2008, 11:43:46) [MSC v.1500 32 bit 
(Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
...    
IDLE 3.0rc2      

>>> print("\N{LATIN CAPITAL LETTER SHARP S}")
ẞ
>>> print("\N{LATIN CAPITAL LETTER S WITH CEDILLA}")
Ş
>>> print("\N{PHAGS-PA LETTER KA}")
ꡀ
>>> print("\ufff0")
￰
>>> hex(ord("ẞ"))
'0x1e9e'
>>> hex(ord("Ş"))
'0x15e'
>>> 

Of course, the exact view cannot be copied, but basically I see very 
similar glyphs for the first two characters, while I had expected a 
"square"-sign or something for the first one; this is what I get with 
other surely unavailable glyph as well as a non existent character. See 
the attached screenshot.

However, the characters remain clearly distinguished, as can be seen 
e.g. after copying them as a parameter of ord(...).

Python 2.6 behaves the same way:
=======================
Python 2.6 (r26:66721, Oct  2 2008, 11:35:03) [MSC v.1500 32 bit 
(Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
...    
IDLE 2.6      
>>> print u"\N{LATIN CAPITAL LETTER SHARP S}"
ẞ
>>> 

...
==============================================

Not that it is much important, but I found it a bit surprising. I'm 
using WinXPh SP3 Czech.