no limit on the number of times you can use the home-sale exempt

http://www.irs.gov/publications/p523/ar02.html#en_US_2014_publink1000200611

How your sale qualifies. Your sale qualifies for exclusion of $250,000 gain ($500,000 if married filing jointly) if the following is true:
You owned the home and used it as your main home during at least 2 of the last 5 years before the date of sale.

You did not acquire the home through a like-kind exchange (also known as a 1031 exchange), during the past 5 years.

You did not claim any exclusion for the sale of a home that occurred during a 2-year period ending on the date of the sale of the home, the gain from which you now want to exclude.