I caught pretty much my first shiny in Pokemon Y (a Cubchoo) today from a horde. The very first shiny I encountered was in Safari, but the odds of finding one there are much easier.
EDIT: A couple of the Pokemon I used in Pokemon Y are now listed as Ubers (Mega Mawile/Aegislash). Should I avoid using them for now on or is using one on your team okay? I read using one on your team automatically makes your team Uber so I don't know.