To make sure everything gets compiled with it, do a full buildworld/kernel (although I think using quick* won't do any serious harm either).
Regards, Sascha
As of
http://gitweb.dragonflybsd.org/dragonfly.git/commit/30c91f0ce501323cf8a9dfdfe46d8c79c7d419b1
GCC 4.4 is now the default compiler.
