To answer your question RE:iphone use while Geocaching, in my opinion the Groundspeak-developed app works very, very well. I am new to the sport as well, and have purchased a Garmin 60CSx for my wife and a DeLorme PN-40 for myself to use in areas with no cell coverage, but the iPhone app works so well in so many places that I have yet to learn to use the 'real' GPSs. I have found around 75 caches in the past couple of months using the iPhone app. It costs $10 in the App Store.
I find that the greatest feature of the app is its ability to locate nearby caches on the go, wherever you are. I travel all over Colorado on a daily basis for work, and it's so simple to pull up the app and have instant access to the 10 closest caches (usually all within a mile or so) and navigate from there. No pre-research required online.
My only complaint is the accuracy of the GPS in the iPhone. It is usually good to get you within 100 feet of the cache, but you'll have to use your geo-sense to narrow it down from there. It hasn't been a problem for me. Occasionally the iPhone GPS accuracy will get to 30 feet, but more commonly I find it at 56 or 156 feet.
Hope this helps.