Yeah i''ve seen this , but to be honest it is too expensive for what it is. compare it to the some of the apps for other instruments and you will see what i mean.
I just found an iPhone app called UkuFingers. There's a paid version for $3.99 and a free version (UkuFingersFree). I just downloaded the free version but I haven't had a chance to explore it yet. You can read more about both apps here: http://web.me.com/ukulele/Uku/UkuFingers.html