The PlayStation Vita will launch in under 2 months in Japan, and when it does, it will be missing some features that may be a deal-breaker for some.
The Vita will launch with most, if not all promised features. However, game archives such as PSOne Classics or TurboGrafx-16 games won't run until later on in the system's life. This may not sound like a big deal, but in Japan the library of PSOne Classics is easily double–even triple–the size of what's available here in the states.
Some good news comes out of Famitsu's PlayStation Vita FAQ – PSP games will be improved via "bilinear filtering" which can be toggled off or on.
The official us.playstation.com FAQ says that the Vita will indeed support PSOne Classics, so many of these features could be added for the US February 22, 2012 launch.