to me the problems the vita presents is one you can't transfer your older psn network games on to it, you have to rebuy them and secondly just how expensive their memory cards are, I may pick one up but i don't know i'm really iffy on it at the moment, granted once a monster hunter game gets released on the vita I may buy ten
The thing is there is actually a way to transfer old PSP games onto the system, the problem is at the moment the method is only available in Japan, and even still you don't get your games for free, but rather using it 'significantly decreases' the price of the game on the PSN store. (I not sure what percentage of a discount it is sadly)
Memory cards I though was a rather sneaky and dishonest move on Sony's part, basically making the item essential to play the majority of the games made it a hidden cost associated with buying the console (not to mention the things are so damn small you can lose them if you take it out of the console)
Other than that the major problem is right now the lack of games people want to play, most of the games are either ports of similar games or sequels that have been done to death. . . my hope is that E3 Sony reveal a deluge of upcoming titles to get people excited, ending on the announcement of a Monster Hunter title.
At the moment the title I'm most looking forward to for the Vita is a title that isn't being release in Japan until next year, so to have to wait until maybe 2014 to get a title to justify the purchase is a little disappointing. . .