|Gold on the Real Money Auction House|
If you do choose to sell gold on the RMAH, then you will take on a 15% fee off the top of the total sale. So if you sell a nice sized stack of gold for $100, you will end up only bringing home $85 (not including additional paypal fees for cashing out). However, let's say that you took the same amount of gold and invested it in an item (or items) that were worth about $100 on the RMAH. If you then sell those same items, you would only incur a $1.25 fee per auction. If you manage to actually sell an item worth $100, good for you, though you'll most likely sell a few of lesser value more easily. So let's say that you sell off 4 items worth $25 each. You end up losing $5 in fees and end up with $95 after the transaction.
Selling gold will probably get you money quicker than trying to sell equally valued gear, but it will also certainly will hurt your long term earnings.
Do you see now how foolish it is to sell gold, at least once players take on a real interest in gear later on in the game? You're much better off converting the gold to gear/weapons and selling those.