Hi Michael - welcome to iDevice astronomy
Yes, I have and like Star Walk as it's better suited to people on our public astronomy evenings than most of the others. It runs a slick display and the graphics are nicely done. It doesn't have any where near the power or number of catalogue objects of either Sky Safari or StarMap, but at the price is a real bargain.
I run it on my iPhone, but I don't think that there is an iPad HD version yet, which is a pity. The augmented reality feature doesn't really work which is also a pity - at least on my iPhone 3GS. For some reason as soon as it's dark, the software complains that it's too dark to image the sky and star pattern - which defeats the purpose somewhat. It kinda works around dusk, but not for long.