Just closed issue 7323 as a duplicate of this one.

I think this issue is worth reopening:  with the backport of the py3k 
correctly rounded string <-> float conversions, there might now be a 
reasonable way to rewrite Decimal.__hash__ so that it's consistent with 
float.__hash__.  Then we can make Decimal-to-float comparisons behave 
correctly and clear up this mess.

I'd still be uncomfortable with allowing Decimal-to-float comparisons in 
2.x but not in 3.x.  Maybe they could be permitted in 3.x too?