One problem I found: You cannot pass variables for pin numbers. I'm not sure what the result is but this does not work...
{
uint8_t i;
for ( i=3; i < 7; ++i )
pinMode( i , OUTPUT );
}
I believe this makes it very likely that most libraries will not work. Without the libraries, you may as well do direct port manipulation.
But I have not tried it, so the problem may not be that serious.