Might be nice to print arrays with square bracket notation. I thought we used to do this, don't know why we changed the behavior (otherwise I'd just fix it myself).
BSONObj o = fromjson( "
{r:[1,2,3]}" );
log() << "o: " << o << endl;
Tue Dec 15 17:54:05 o: { r:
{ 0: 1, 1: 2, 2: 3 }}