The FAQ notes that Sony is "considering" a service to offer PSN versions of the UMD games users own for a "special price." This isn't a confirmation, but at least Sony is looking into some method to make it possible to play the UMD games you bought on your Vita. "Details of this service will be announced at a later date." That's the good news.
The bad news: the FAQ says that the Vita will play all downloadable PSP games ... except for Game Archives, which is the Japanese label for PSOne Classics, Neo Geo games, and other retro downloads. Sony will have more details about this limitation later, but the fact that there's more to it than "they all work" is troubling. We really hope we'll be able to play the PSOne games we've already bought ... and that we won't have to buy them again in their Android/PlayStation Suite incarnations.
Sony PlayStation Portable PSP-2000