Siliconera notes that this is roughly 3/7 of the total PSP games currently on the PSN for download. (Well, they give the numbers themselves; I provided the fraction, because fractions are awesome. Who can’t immediately visualize 3/7?)
Square Enix, Capcom, and Namco Bandai haven’t joined in yet, but this list isn’t comprehensive; Sony’s original news regarding the UMD Passport program listed Falcom (and Square Enix, for that matter). I figure it will be updated as they work out the licensing arrangements with the various developers.
That said, I’ve decided to bite the bullet and get a PS Vita at the US launch (using a combination of various credits, coupons, game trade-ins, and the like to lower my price at amazon by a great deal). I’ll probably just pick up Uncharted: Golden Abyss from the US launch lineup; I’ll also have Tales of Innocence R (which releases in Japan ~1 month before the US system launch), and with Growlanser and Disgaea, that should keep me busy for some time.**
*For Japan, at least.
**When I’m not losing my mind at law school, anyway. I think a portable system will be convenient for between classes; I’m more likely to have time to game there than at home, and I can’t study all the time.