Ok so we tried this one out and WOW! Its amazing. My son loved it. My only complaint is that when doing the placement test my son found the sound for the wrong answers more enteraining then the correct ...
That's funny! We have been doing Readingeggs since January (My son is 4.5 yrs old now) and I have had the same problem a few times. Especially with the ninja who climbs a fire escape REALLY SLOWLY when you get the right answer, and then races down SCREAMING when you get the wrong answer. After my son had done it twice, I told him he could get the wrong answer only when he had done one or two correct answers, not near the top, as it is so painfully slow to start from zero again! I wrote the Readingeggs feedback on site to tell them this. That they need to make the wrong answer "feedback" to the kids WAYYY more boring than the correct answer rewards. Even still, my son will often point to the correct answer, then say out loud "I wonder what happens when I press the wrong answer?" and try it out. It helps me to take it less personally when he seems to purposefully do something wrong or against my instructions in daily life!

! I figure it must be the same thing. He knows the rewards for the correct behaviour and is just dying to see what will happen if he does the wrong thing. "what will mommy DO?"
Anyways, we have been doing the Australian version (we are in Canada) for five months now and my son still loves it and requests to do more... we are on map five, having finished 44 lessons so far. The major problem I am having is with flash animations, ie when one must click on a letter that moves all over, or push a fish or a cloud with a word or letter across the screen. Often on our mac it is very hard, and doesn't seem to recognize our clicking or dragging, and I have to send him to do something else for a few minutes, as I try to do that part of the lesson myself. Even at over 40 yrs old, I find that frustrating enough to pull my hair out, so imagine being four. It works best I imagine, on a pc and the latest version of flash.
But all in all, we love it and my son has learned sooo much.