just chiming in that i too absolutely love my vita. i game on it more than any handheld i've ever owned, and often game on it when i could be gaming on the tv. the library isn't huge yet, but there are certainly enough games to keep you busy (i play it a lot and have barely scratched the surface).
plus there are several games on there that have infinite replay value for me (pinball arcade, super stardust, lumines, sine mora, zen pinball, etc).
and when you throw in psp and ps1 classics the library is, in fact, massive. both psp/ps1 games look fantastic on the vita -- and while my psp generally gathered dust my vita never does.
the OS is quite nice - you can insta-pause any game and then use the browser, check trophies, etc, concurrently.
download speeds - someone here complained about them. mine are fine. ymmv, but i see no difference between my vita and any other device.
ps+ - imo a must buy. heck, you get uncharted, gravity rush, and many more games (and later this month disgaea 3) for $50 for the first year... it's certainly worth that just to play all those games and you'll get to decide in a year if you want to extend. if you already have ps+, then the vita is an even easier buy.
memory cards -- i bought a 32g and am glad i did. yes, i paid $75 for it. yes, i wish i only paid $10 for it (obviously). but even if expensive, i consider it a great purchase since it makes a great device even better. i have it stacked with around 20 vita games of various sizes, 15 minis, 15 ps1 games, 10 psp games, a handful of demos, and then various apps like skype, netflix, youtube, etc.
i realize everyone wants the price of the vita and mem cards to come down, and financially, i understand why. but even at current prices, it's a great value if you can swing it. sony outdid themselves with this thing, and if integration with the ps4 is half what they promise, it'll just be icing on the cake (full remote play for all ps4 games? yes please).