I'd imagine that even if you trained hard but not to failure 3 times a week for a year, you'd still gain a lot more muscle mass than someone who trained to failure every now and then. If you don't like training to failure, don't do it. Personally, it's something I try to do most of the time, although nowadays it means that I only work those muscles a couple times a week and then work on something else during my 3rd weekly workout with weights. The big thing you *don't* want to do from what I gather is overtrain, that is, work out when you're still sore or work out past the point of failure and to the point where you actually get injured.