The FLAC sourceforge project has made its last release for Windows in 2007-09-17.
The darwin release dates from 2009-04-09.
My conclusion is that FLAC development has stopped in beginning 2007, with ports being the only activity since. Although it's still in use, no new evolution is to be expected.
You may have a look at the FLAC-News section of the FLAC site. The latest news dates from 10-Dec-2008 of Paul McCartney's side project The Fireman releasing its new album Electric Arguments as a digital download, and available in FLAC.
So the FLAC codec is still in use, and will stay supported by current players for many years yet. But its use will die out with time.