Potential pitfalls when going from old-style to new-style classes

[Skip Montanaro]

I discussion on the code-quality list got me thinking. Suppose I have
an old-style class in a 2.x app:

class Foo:
  def __init__(self):
    blah blah blah

I still use 2.x exclusively, but anytime I run pylint over a bit of
code and it complains that Foo is old-school, I make the obvious
change to inherit from object. While I do this mostly to shut up
pylint so I can focus on more serious messages, I must admit I have
never experienced any problem changing from old-style to new-style
classes. Under what circumstances might this be problematic?

Thx,

Skip