You know, the camera on my 3Gs is an absolute and utter piece of shit in many situations and the only way that I can make the images useful is to pull it into another app and tweak the contrast/brightness and saturation... so my vote would be to get the 4. But your wallet will determine what you can purchase
And remember, next summer they're likely to unveil a RAM-enhanced version of the phone, so if you want to keep a lot of photos and music on your machine you might want to continue limping along until that refresh... or maybe the one after that?
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