Oddly enough, I just finished with my taxes - did you know you can actually pay it back ahead of time if you want? I am paying back $500 out of the $7500 this year, but they gave me the option to pay any amount I wanted to, just had to be a minimum of $500.
This credit wasn't a big factor in our decision to buy a home - but we also used it wisely. We bought in Sept 2008, and after we got our $7500 back in March 09, we turned around a refinanced from 6.5% down to 5% - I figure we'll save about $60,000 over the life of the loan, worth taking an interest free loan from the government for! The $7500 more than covered the closing costs for the refi.