A good summary of a lot of the pros and cons:
http://www.chabad.org/library/article_cdo/aid/1507393/jewish/Is-It-Okay-to-Celebrate-Bin-Ladens-Death.htm
A couple of key paragraphs:
For the same reason, Solomon tells you
not to rejoice over the fall of your
enemy. If that’s the reason you are
celebrating—because he is your enemy,
that you have been vindicated in a
personal battle—then how are you
better than him? His wickedness was
self-serving, as is your joy.
But to rejoice over the diminishment
of evil in the world, that we have
done something of our part to clean up
the mess, that there has been
justice—what could be more noble?
...
So there’s the irony of it all, the
depth and beauty that lies in the
tension of our Torah: If we celebrate
that Bin Laden was shot and killed, we
are stooping to his realm of
depravation. Yet if we don’t celebrate
the elimination of evil, we
demonstrate that we simply don’t care.
We are not angels. An angel, when it
sings, is filled with nothing but
song. An angel, when it cries, is
drowned in its own tears. We are human
beings. We can sing joyfully and mourn
both at once. We can hate the evil of
a person, while appreciating that he
is still the work of G-d’s hands. In
this way, the human being, not the
angel, is the perfect vessel for the
wisdom of Torah.