Falcom's support of the Vita, most notably Ys Celceta: Sea of Tree's

Really, if this is even half as good as the PSP for me, then, there's yer reason. There's alot of great games on the PSP IMO, & that'll be the reason to get a Vita. At the very least, I'm sure Uncharted is great. If you like Katamari, there's a new one of those for it. Ofcoarse, since I don't have the system itself yet, I can't comment on the quality of the hardware & how durable it is, etc.
But, really, it's mainly about Falcom, even if some of the games don't get translated, I'll still buy their Ys games at the very least!