The Vita is a handheld system that is the 2nd generation of the PSP, so it doesn't make sense to compare it to the PS3, despite costing more than a PS3.
Overall, I would wait on buying a Vita. It's still very new, and therefore, untested.
It's expensive. Just the unit itself is almost as expensive as a PS3, then when you throw in one of Sony's proprietary memory cards (required) and other accessories, like a case, you're up to nearly $400 and you still haven't bought any games yet!
The games are expensive. $50 for a handheld game?!? Are they kidding? And so far there only seems to be one game worth getting - Uncharted. This isn't too surprising since all new hardware platforms suffer from a small library of "must have" titles for the first year or so that they're on the market.
While the Vita is compatible with older PSP games, you have to buy them online through PSN. The Vita has no UMD drive, and Sony is not offering its UMD-exchange program in the US. This means many excellent but UMD-only PSP games will disappear into obscurity. Even those PSP titles that are available through PSN retail at full price, $30, even though the same game on UMD is available in stores for $20 or less.
Despite being more advanced, the Vita still relies on the same broken, PC-only software to transfer music, videos or pictures to the Vita. In this era where every smartphone simply shows up as a USB Thumbdrive without needing any special software, this is just inexcusable.
Also, the Vita still uses the same limited, slow, broken web browser that the PSP and PS3 use. The DSi and 3DS' browsers are much, much better.
I would really recommend waiting for the first price drop to occur, which will mark the first major revision to the Vita. You should get a better product for less money, and most likely you'll be able to find some good bundles that should throw in a memory card and a game at least.
The big video game trade show is scheduled to happen at the end of May. If there are any major announcements about the Vita's pricing or bundles, they'll happen during this show. So I would at least wait this long before making a decision.