Pennsylvania Inheritance Tax

If I have a Philadelphia County registered same-sex relationship can I
avoid the Pennsylvania Inheritance Tax?

No. Unlike the Commonwealth of Pennsylvania of which Philadelphia is
part, Philadelphia has recognized domestic partnership status and
allows partners to register formally as domestic partners. Philadelphia
then recognizes the couple as married for tax issues such as real
estate transfer taxes. Unfortunately, the Pennsylvania Inheritance
Tax is a Commonwealth Tax, not a Philadelphia Tax, so Philadelphia's
recognition has no effect on the Inheritance Tax. This means that
instead of paying the 0% married couple inheritance tax rate a registered Philadelphia domestic partner will pay the 15% rate of inheritance tax between unrelated persons.

Civil Union in One State, Divorce in Another...

If I have entered into a New Jersey civil union with my partner, but
now we are Pennsylvania residents, can we get a Pennsylvania divorce?

In limited circumstances when both parties are in complete agreement
Pennsylvania courts have dissolved same-sex marriages and civil unions
but when there is not complete agreement the parties are not allowed
to use Pennsylvania courts. To get your divorce you have to return to
New Jersey, or whatever state created your same-sex marriage, civil
union or domestic partnership, become a resident then file for divorce
or dissolution. This is a changing area of the law, so don’t be surprised if in 2012 or sometime soon after this answer changes.