Depends on the beer type you're trying to make and the AA of your hops. Personally, I've used about 1.5g/L recently on an IPA with some galaxy and Citra and it's nice and hoppy to my tastes/nose.
I dry hopped a pale ale in a keg with cascade and found it too over powering, so I possible should have aided the dry hops to the fermenter or secondary and only for a few days, but that just might be me and my pallet (it is learning )
But I went to transport Bar satdy night and had a pint of alpha pale ale (well maybe a few I tried as many beers as possible to see what I liked and the alpha was the only one I would go back to) and that was very "strong" on cascade aroma