between .9 and 1.2 g/lb of protein has worked well for myself and my colleagues that have gained muscle without getting fat.
I can't comment as to the efficacy of eating more than that, but I can comment on eating less. Up until about 18 months ago I consumed somewhere around .6 to .75 g/lb, and didn't see much growth in terms of muscular strength, explosive power, or size. I ran through the gamut of programs, but it became abundantly clear my error wasn't training, it was diet. It wasn't until I really started eating over 3,000 calories in the form of 5 high protein meals throughout the day that I was finally able to break through some barriers.
The elimination of high glycemic load demons helped tremendously as well.
I guess it depends on everyone's individual goals, but for anyone looking to gain muscle mass I would endeavor to get as close to 1 g/lb as possible. Whey is the word here.