Spare my Liver
I used to play the Fried Liver myself - that was until i learned that sometimes, the priority of development overweighs a meer pawn.
The Fried Liver seems to be especially popular in junior events. But seriously, and I try to say this in the most polite way I find possible to get the message across - you gotta MOVE ON sometimes in your chess-playing career! There are way better things to do in the opening than to hope that your opponent will play 5...Nxd5, just so that you can sac a knight.
4.Ng5 is almost never seen in top tournament play. The reason is simple first of all - which master will be ever so stupid as to play 5...Nxd5? Secondly, there are way better ways to get an advantage in the opening phase. Grandmasters don't think of a pawn as an advantage! Otherwise what's the use of inventing gambits?
Here are two games from the Fried Liver.The first of which is the complicated Wilkes Barre variation. Instead of 5 Nxf7, Bxf7 + would be better as it cuts down the amount of theory. The second game is the one which stuck to the main line.