I am very interested in this question, but would never Grob in a normal game I play. (English, Sicilaian, Riti, Queens games is how I tend to play)
If you would like to play a game (rated or Non rated) I would be glad to let you be white or black and try this move g4 and see where it goes. I will also use data base etc. to follow some lines I find and like (I don't during my online games) and share notes if you like.
My (albeit limited) understanding of the grob is that it works best in OTB games, often because the surprise factor can cause your opponent to waste time trying to figure out the best move to counter it, since the opening lines for black don't follow traditional king's or queen's pawn opening. In a correspondence game you'll probably get trounced, since there seem to be fairly easy responses for black that result in fairly solid control of the center, all black has to do is have the time and resources to look these up.
I imagine the goal for white is to develop queenside pieces and then queenside castle ASAP after fortifying the lone g file pawn. If your opponent castles kingside this will allow you to push pawns on the f, g and h files and compromise his castled position. Like any other opening, you can probably win some games with it, but there's likely a reason why we don't see it too much in GM play.
-mike