This is totally anecdotal, and I can't say for sure that the Arginine is what's making the difference, but I've been taking 2 g of arginine in tablet form off and on for several months. I recently became complacent (stopped taking it for a week or so), and around the same time my morning woods became weaker and/or went away. I'm back on 2 g per day for the last 3 days, and morning woods and EQ in general are now through the roof. This could be related to natural cycles and/or other lifestyle factors, but it's worth taking note. not2big also mentioned 5 g per day helped him, so maybe start with 2, give it a week, and go up a gram a week until you notice a difference?
I've never taken citruline, so I can't speak to that.