We have not sealed the grout here in TV because someone told us sealing the grout would void the warranty, and we just moved in 2/1/12.
Up north Stanley Steemer sealed the grout, and they offer to come back to steam-clean the same tile whose grout they sealed, so I assume steaming does not remove the seal.
In any event, the Shark home machine is not heavy, industrialized equipment as Stanley Steemer's, and I can't imagine it taking the seal off of the grout.
We are having our TV great room tiled in the fall. After the one-year warranty is up on the house in 2/13, I plan to have SS come in and clean all the tile and seal the grout. What they did in our house up north has held up so well, and our kitchen up there gets a direct hit from us walking through the snowy, slushy garage (at least up until this last year
)