Our grout was so stained (previous owners) that no amount of cleaning would take care of it. We had it colored (painted), and it turned out great. It's yellowed a tiny bit, but just being a consistent color makes it look tremendously better.
Before that we tried bleaching, scrubbing with SnoBowl and other cleaners, and steam cleaning. Nothing worked very well.
"Good judgment comes from experience. Experience comes from bad judgement." - Will Rogers
DW and I - FIREd at 50 (7/06), living off assets