These should all return False, or some of them should raise exceptions:

Python 2.6.2 (release26-maint, Apr 19 2009, 01:58:18)
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import decimal
>>> decimal.Decimal('0') > 0
False
>>> decimal.Decimal('0') < 0
False
>>> decimal.Decimal('0') > 0.0
True
>>> decimal.Decimal('0') < 0.0
False
>>> 0.0 > decimal.Decimal('0')
False
>>> 0.0 < decimal.Decimal('0')
True
>>> 0.0 < decimal.Decimal('0.0')
True
>>> decimal.Decimal('0') > decimal.Decimal('0')
False

Unfortunately there's no easy way to fix this in 2.x, where any object is 
supposed to be comparable with any other.  See issue 2531 for a previous 
discussion.  It's fixed in 3.x:  there a comparison (other than ==, !=) 
between a float and a Decimal does raise an exception.

Closing as a duplicate of issue 2531.  Issue 2531 is also closed, but you 
should feel free to add to the discussion there.

I've re-opened issue 2531:  some recent changes (in particular, the 
backport of the 3.x float <-> string conversions to 2.x) may make 
previously rejected solutions viable again.