[danielharan]

I'd use a snowball, to convey the growing nature.

[waheoo]

Or just say what it is, compounding growth.

You guys always gotta make stuff more complicated than it is.

[gk1]

The English language is full of idioms and metaphors; marketers are hardly the only ones using them.

Actually "snowball" probably makes more intuitive sense to people than "compounding growth."

[perl4ever]

A snowball rolling down hill is a metaphor for compounding growth.