I don't have an iPhone, but I'm becoming a pretty big fan of EveryTrail.com since I first used it to post the GPS data and photos from a hike in Acadia(Giant Slide) Anna and I did... and it turns out that they've released what seems to be a really cool application that allows you to use your iPhone to get GPS data and synch up photos you take so that you can post them on the site. I have no idea how well it works, but the convenience factor of only needing your phone to GPS a walk/hike is pretty sweet.
The major problem I see with it, is that(I presume) you need cell phone service to use it... and in Acadia, at least, service is spotty at best. Though, on the other hand, if you just want to GPS your vacation and be able to localize your photos on a map and put them in context, I can't think of anything that would be easier that this. I'm not quite oblivious enough to wear my Forerunner when walking around in Sienna or something... but I certainly wouldn't mind using this application... if I had an iPhone... or were in Sienna. But, you get the idea.