Well I got my new iPad yesterday, and I am completely in love with iPad all over again. My original iPad was getting frustrating because apps were crashing regularly and it was slow to switch between apps (all due to memory in my opinion, not the A4). So I am completely stoked!
I did a quick compare with my wife's iPad 2 last night, and speed wise there is nothing in it, they seem identical. The screens look worlds apart though - the iPad 2 seems washed out by comparison, and seems to have more 'leakage' if that makes sense, but I never noticed this before getting the new iPad.
My advice would be, if you're going to get an iPad 2, don't spend too much time with the new iPad, because once you have, the older screen will look worse than it really is.
One last thing - the weight really isn't an issue if you're used to the original, but the iPad 2 is noticeably lighter when holding in one hand.