Lady GaGa has made dance music mainstream - DJ Tommie Sunshine

[FaRmLaNd]

I can't speak for the US but in the rest of the world "dance" music and electronic music has been popular for a VERY long time.

A lot of Electropop was popular in the 80s and people like Kylie Minogue and Madonna have been doing it since before Jesus was born.

Of course Lady Gaga is leading the resurgence.