Interesting topic, and one that has much controversey and debate surrounding it.
Personally I rarely train to absolute failure (the inability to execute another rep of the exercise). In fact, I only do so when I am testing myself (be it maxing out, or seeing how many reps I can do of a particular exercise).
I used to train to failure a lot more frequently, but honestly didn't really see any stellar results from doing so.
Lately I have been training more in line with Chad Waterbury's High Frequency paradigm, and have seen great improvements in both strength, and I have also seen improvements in muscle mass (although that is not my primary goal).
I currently am only training every body part 4 times per week. But may increase that to more, not sure yet.
In my experience, training your body parts infrequently (every 4-7 days) isn't as "sure fire" a method for gaining hypertrophy as many in the industry would lead you to believe. Will it produce hypertrophy? Sure. But will it do it better than training more frequently? Not in my experience.
I think the question that you need to ask yourself is; why am I training to failure? Do you really understand the mechanics of doing so, and what are the benefits?
But, hey that's just my opinion.