Yes it's been done before but it doesn't make it any less cute and nerdy to me. My now fiancé proposed to me on the front cannon turret of the historic WWII Liberty Steam Ship the SS Jeremiah O'Brien with this, I squeed!
Check out these wedding bands by Sakurako Shimizu. They are molded into a waveform representation of your partner's voice recorded saying "I do," or any phrase you choose. A very cool and unorthodox idea!