Yes I did. I used Fila Porcelain Impregnator/Sealer before and after grouting. The first application was with a foam roller which left a very bubbly layer. When dried there were a lot of dark spots where the bubbles were. You can't see them unless you are on your hands and knees though!
Grouted with Mapei black the applied second coat using a brush giving a smoother layer. Getting residue off was a pain and I eventually used kitchen roll with a dab of sealer on it to wipe it off before polishing with dry kitchen roll.