The key here is you have to have been in contract by April 30 of this year. If you were, they are giving you until September 30 of this year to close and take advantage of the $8000 tax credit for first time home buyers and $6500 credit for homebuyers who are buying a new primary residence.
The first tax credit that was to expire June 30 of this year has caused some back log with buyers trying to meet that deadline. This new deadline to September 30 should give everyone some breathing room.
Read the Reuters Article lining out the details of the extention.