I use a lot of kettlebell swings and snatches as part of my training programs because they are highly-effective. Not only do they develop strong, powerful hips, but also develop torso stability and burn a ton of Calories (many, many muffins worth). As, kettlebells gain popularity, I see more people using them improperly. Their poor mechanics leave a lot to be desired. However, when done properly, your glutes and hamstrings should bear most of the stress, not your lower back. With a little patience and proper timing you can save your back and see great results.
One of the most prevalent issues with the mechanics of the 'hip snap' is when you exert a pulling force on the handle too early and too long in the swing phase. This not only puts more stress on the lower back, but is inefficient, as it projects the bell forward. This has two consequences. First, it pulls you onto your toes (which diminishes activation of your glutes and hamstrings). Also, the bell is now on a curved path, which is bad for a clean or snatch (think bruised wrists and clavicles)!
So, stay back on your heals and wait for gravity to move the bell forward, just in front of your knees, before you apply a quick, aggressive hip snap.