TW - Balloons ARE regulated in the USA.
Indeed! FAR Part 31 is dedicated to "Airworthiness Standards: Manned Free Balloons". FAR 21.21 and 21.183 (airworthiness & certification) apply to "manned free balloons" as well as other aircraft. So does FAA Order 8110.54 (Instructions for Continued Airworthiness), which has sections dedicated to balloons (e.g., Sec 4-5).
Heli-phile: What other regulations do you think are needed? Where is Part 31 lacking?