Yahoo recently posted an article on some common estate planning errors that points out certain issues that should be considered when establishing an estate plan. http://finance.yahoo.com/news/don-t-common-estate-planning-115556072.html
There are plenty of other pitfalls to be avoided which emphasize the need to consult with an attorney.
As many people are aware there currently exists a $5.25 Million portable Federal Estate Tax Exemption. It allows spouses to effectively protect up to $10.5 Million from Fed. estate tax. However, for example, what happens if you pass away before your spouse and that spouse re-marries then dies? The new spouse could end up with all YOUR MONEY and leave nothing for your children, family members or friends!!
A well formulated estate plan can protect against such results.