Actually I don't think you need a review from someone that owns one to form your own opinion. Lets look at the technical differences to see why. There are only 2 legit differences.
1) A5X vs the A6X CPU/GPU.
2) 30 pin vs lightning.
The connector to me is a wash and doesn't add anything to the conversation. So lets get to the real issue and let me start out with my opinion and the technical basis behind it.
For the first time ever, I can say beyond a shadow of a doubt, no it is not worth upgrading from the 3 to the 4. So now for the why.
Does the speed of the new CPU and GPU justify an upgrade? There are no apps currently in the App Store that need the new speed. Will there be? Oh yes. Games first and probably will be out very soon. But mainstream apps? Not a chance. The iPad 3s speed is more than enough to handle any 3D modeling like Google Earth and is overkill for Web browsing, Flipboard, Pages, Numbers and a lot of other productivity apps. In fact it can handle any of the top 1000 non-game apps with speed to spare. So let now look at the "how long" portion of the situation.
There are currently 5 mainstream devices that are slower than the iPad 3. The iPod Touch 4. iPhone 4/4S and iPad 2/Mini. They all run on either the A4 or A5 processor. The sheer number of them currently out there means that developers have to keep that in mind to generate the largest revenue base. If they targeted the iPad 4 only, they would have an audience only in the millions. The devices I listed combined are closer to the 100 million and that is in daily use.
Remember, my analysis is based on what I believe the developers will be targeting for the next year. If you for one second think they will switch to the speed of the iPad 4 immediately and you want to be able to use the applications at full speed, then yes an upgrade can be justified. I personally will wait for the iPad 5 before I upgrade my two iPad 3s.