GAAP is one of 7 standard was of doing accounting, if your company is publicly listed (US stock exchange) then you must use GAAP, other wise ....

see this for more on GAAP,  http://onsale-apparel.com/Rustler/gaap

But first your friend is full of it, second yes if you wanted to use GAAP in QB you can do so, there is no reason to, but you can