Hehe had one from the first launch here, it is the greatest single device I have and for me it eliminates the need for a laptop. Most users - self included - go through a phase where they collect a lot of apps, try them out then trash most of them when the novelty wears off. Favorite apps:
Mating Call
probably the most important of all...
OzWeather - excellent weather app, it uses the latest BOM data and accesses the data from the AWS stations in each state. Far more accurate than any other for local forecast data and it has been pretty good at predicting weather 1 week out.
Emerald Chronometer 'Mauna Kea' - the most sophisticated "watch", it syncs with GPS time, shows sunrise/set, moonrise/set, moon phase, twilight, siderial time, the zodiac constellations in real time, GMT and more, all on one dial. Then there are the other watches that come with it, but I don't find them useful.
i41CX - full emulation of the HP41CX calculator, and then some, it means I can quickly program the iPhone to do something simple.
StarMap Pro. The best iPhone ephemeris by a wide margin, it is specifically designed to use in the dark at the scope and clearly was designed by an experienced observer.
TouchFS - for storing and viewing files on the iPhone, mainly PDF's. I have PDF star charts and other reference materials on it as well as other work-related stuff.
Clinometer - use it for leveling the tripod, checking the altitude of the polar axis and more.
Domain - for looking for a place to live, works very well compared to hunting online.
Remote - for driving my AppleTV or iMac from the lounge
And a bunch of games but I'll refrain from boring you there.