Here's the example they site:
Example #1 — Lt. Green owned a house in Georgia and lived there from December 1988 until deployed overseas in January 1991. When he returned to the United States in July 1999, he was stationed 90 miles from the house. Preferring not to commute this distance, he sold the house four months later, realizing a gain of $150,000. Because he had not used the house as his principal residence during the 5 years preceding the sale, he reported this capital gain on his 1999 return. Under the new law, he can disregard both the 8½ years he was overseas and the 4 months after his return to the States, since he was stationed more than 50 miles from old residence. His five-year test period for ownership and use now consists of the 5 years before January 1991, when he went overseas. Since he owned and lived in the house for more than two years during this test period, he may exclude the gain on the sale. He must file an amended return by Nov. 10, 2004, to recover the capital gain tax paid on the 1999 return.This law went into effect in 2003, but I just recently heard about it. It's a great tool for military families who own a home from a previous assignment.