The problem with a thread like this is that people will give you an answer which is designed to justify their own purchase. Nobody likes to feel that they've made a bad decision.
My situation, is that I took my iPad 3 back to Apple for a refund at the weekend, because I didn't feel that there was enough of a leap between it and my iPad 2. The Apple employee that processed my refund seemed to agree, saying that she had not made the jump from iPad 1 for the same reason.
In truth, the screen is slightly nicer, but in my opinion, that is due to the colour saturation as much as the resolution.
As someone else said in this thread, people were more than happy with the iPad 2 screen a month ago, and the other so-called improvements in the iPad 3 are very slight.
I suppose it boils down to how much disposable income you have, and whether you feel you'd rather have a slightly higher resolution screen on your iPad or an extra £100 in your bank account for other things.