Trusts and Estates published an article here called Get Me To The Church On Time by John T. Brooks and Samantha E. Weissbluth.  They write:

"The Kinney case out of Minnesota offers a good review of the general requirements for a valid prenuptial agreement. The appeal also shows a modern trend in which courts view such agreements with suspicion when one party is not represented by counsel. Of course, decisions in most cases turn on the facts, but courts tend to enforce prenups when the playing field is more level. The litigants in Kinney appear headed for another round to determine the facts and fairness of the agreement. Estate of Kinney, 733 N.W.2d 118 (Minn. June 14, 2007)."

The leading case in Pennsylvania on the enforceability of pre-nuptial agreements is Simeone v. Simeone, 581 A. 2d 162 (Pa. 1990).   The case marks a sea change in the way Pennsylvania courts viewed these agreements.  The PA Supreme Court abandoned the protective and paternal stance of earlier years and provided these two requirements for enforcability:

1.  application of the usual contract law concepts about invalidating contracts for fraud, misrepresentation, or duress.

2.  a "full and fair disclosure of the financial positions of the parties"

Notably, the PA Supreme Court did not require representation by separate counsel:  "To impose a per se requirement that parties entering a prenuptial agreement must obtain independent legal counsel would be contrary to traditional principles of contract law, and would constitute a paternalistic and unwarranted interference with the parties’ freedom to enter contracts."  See Simeone at p. 161.

Despite the assurances of Simeone, I have never been comfortable with a pre-nup unless both parties are represented by separate counsel.   I have always insisted on such representation for the party who is not represented by Spencer Law Firm.  Call me paranoid, but I think the Kinney case in Minnesota points out the risks and it can happen here in Pennsylvania too.
 

Additional resource:

Robert B. Standler has an excellent essay, Prenuptial and Postnuptial Contract Law in the US, posted at http://www.rbs2.com/dcontract.pdf.

Postscript:

I never refer to these agreements as Antenuptial Agreements, although that is quite proper and correct.  I find that the general public’s understanding of Latin is quite deficient.  Many do not know that "ante" means "before" as in "antebellum."  All too often they mistake it for "anti" which means "against" as in "anti-aircraft."   We don’t want them to think these agreements are "against" marriage.  On the contratry, they are a way to promote marriage with the parties making their own property agreement instead of relying on the "one-size-fits-all" agreement provided by state law.