Negatives
-OS is already dated (Jelly Bean time!) and will likely stay that way for at least another 1/2 year if you're lucky. If you're unlucky, by this time next year you will still be on Ice Cream Sandwich, still waiting for Jelly Bean with no official word yet from Google or Samsung, with newer phones coming out with Key Lime Pie.
-can be laggy at times, freeze, and restarting/pulling battery is a technique you will master
-still not as wide a selection of apps vs. iTunes
-switching over, all your drm-protected iTunes music and apps are worth squat
-still new, don't know if there will be problems, ala GPS fiasco?
-iPhone has more accessories
For me it's a toss up. I switch between wanting to buy the GS3 now and waiting until the iPhone 5 comes out. With the GS3's OS already dated, I'm gonna wait till the iPhone 5 comes out to 1) see what that's all about 2) see if the GS3 will get Jelly Bean and 3) if not, what other flagship phones with Jelly Bean are available. I like iOS 6, it's got some interesting features. If the iPhone 5 doesn't wow me and I know the GS3 will not get Jelly Bean that quickly, maybe I can hope for a Verizon Galaxy Note 2 with Jelly Bean....