[russss]

People do use hydrogen, but most balloons still use helium because it does provide a slight safety advantage when launching. (It's also sometimes an insurance requirement.)

I expect to see an increase in the number of hydrogen-filled balloons as helium prices rise in the next few years.

[malandrew]

That makes sense. Helium seems to be too precious a natural resource to be using in applications where hydrogen can be used safely.