You’ve seen the story of Larry Walters, who achieved an altitude of 16,000 feet with a cluster of balloons. Did you know that Cluster Ballooning is now an extreme sport? John Ninomiya is the only regularly active cluster balloonist in North America, and there are about a half-dozen others worldwide.
Cluster balloons, like all balloons, are aircraft that require skill and training to operate safely. Before I began flying cluster balloons, I was an FAA-licensed hot-air balloon pilot and had over four-hundred hours of pilot time in conventional hot-air balloons and Cloudhoppers. These skills are not rocket science, but they are NOT something you're going to figure out on your first flight while you're drifting toward the high tension lines and imminent crispy-critterhood! Fly safely!
Link -via Ursi’s Blog