It's used in Gipsy/Flamenco music ... Also there's a more awkward tecnique for speed picking , and I'm sure it's very widely used too.

M I m i
e-0-0-0-0-

This is not what you think , the first M I is done normaly , while the other 2 notes m i are picked by the BACK of the finger (nail).
It's similar to rasguedo (spell?) technique , but on one string ... Very hard though !

To do this technique, you gotta have tall nails .