Something else to think about.

If say community service by Obama's definition was say for example helping build a road.

The average road worker makes $38k a year

$38K/12=$3,166 a month
$3,166/4=$791 a week
Assume a 40 hour work week
$791*2.5(for 100 hours)=$1979

So where does the other $2,021 come from to pay for the $4,000 tax credit?

It would have to be ~200 hours to break even.