object.c.doc

Equality---At the Object level, == returns
true only if obj and other are the
same object. Typically, this method is overridden in descendant
classes to provide class-specific meaning.

Unlike ==, the equal? method should never be
overridden by subclasses: it is used to determine object identity
(that is, a.equal?(b) iff a is the same
object as b).

The eql? method returns true if
obj and anObject have the same value. Used by
Hash to test members for equality.  For objects of
class Object, eql? is synonymous with
==. Subclasses normally continue this tradition, but
there are exceptions. Numeric types, for example,
perform type conversion across ==, but not across
eql?, so:

   1 == 1.0     #=> true
   1.eql? 1.0   #=> false