While not up and running yet, it looks like Sony is quietly testing the often-demanded service. US users can now actually download one PS One title to their Vitas, getting past that annoying "Cannot download using a PS Vita system" message.
However, the game, Buzz Lightyear of Star Command, doesn't run yet on normal Vitas - guessing it does on Sony's internal development firmware, when that goes live all those classic games will come flooding back to life with twin sticks and upscaling. the game doesn't appear on the PAL store, so no luck us, yet! A tiny bit more on VG24/7.
Is it too much of a leap to think that today's PSN downtime (starting to wonder if it is ever really up?) is a pre-cursor to activating the feature?