It is indeed very nice to finally see cacheable topo maps on the iPhone. However, a tracking feature would be pretty useless because you would have to keep the app open, which would drain the battery in 2-4 hours even with the screen dim (according to reviews of the other GPS apps). You cannot use the GPS while in flight mode, which means you must keep the cellular antenna on whenever you use the GPS. This adds considerably to power drain.
Further, I can't get the MotionX GPS or GPS Kit apps to track while in 'suspend' mode (i.e. tap power button to turn screen off), so I doubt iTopoMaps will be able to either. The app would have to enable background processes to access the GPS, which Apple forbids. That said, my old Pocket PC and Windows Smartphone devices, which did allow background processes, couldn't track while in suspend mode either, so it may be even more complicated than that. Thus, to use tracking, you have to keep the program open and running, with the screen and cellular antenna powered. Not a formula for reliable tracking, and nothing an app programmer can do anything about.
Thus I see the biggest benefit of GPS-mapping phones in general as locating yourself on the paper map without the need to plot coordinates. Turn the device on, find your position, compare it to your paper map, and turn the phone off. This simplifies the process of finding yourself on your paper map, but is still a supplement to a paper map. This also is the best use of the phone anyway, as it would minimize battery drain.
Unfortunately, however, the iPhone's GPS isn't that sensitive; it can take a while to find your location if you turn it off. I was impressed that I was able to get a signal in a pretty dense forest here in Western Oregon, but it took almost 5 minutes to lock. This limits its real-world usefulness as a primary navigation unit compared to the high-sensitivity receivers out there. Hopefully Apple will improve the GPS hardware in the next version, or at least allows GPS access in flight mode.
Don't get me wrong; I would love to have an all-in-one color mapping GPS device. But after 7 years of frustrating disappointments with PDA-Phone-GPSs, I finally realized that the simple, slow processor and non-backlit daylight display in something like the Garmin eTrex series is the only way you're going to get good battery life with today's technology, and the waterproof, ruggedized casing with replaceable lithium batteries with is the only way you will get reliable performance in the harsh conditions in which you would actually need a GPS for survival.
Thus, I broke down in January and bought a Garmin eTrex H; my first ever non PDA-phone-GPS, and the simplicity and ease of on-the-trail use are frankly refreshing. If I want to mark a waypoint, I press and hold a button and press confirm. No powering devices on and off, no turning radios on and off, no removing gloves, no worrying about the quality of the Aloksak zipper.
I do like audiobooks on the trail, so I debated getting an iPod Shuffle and leaving my iPhone at home, but since the iPhone has twice the audio battery life and includes a cell phone for roadside assistance or lucky reception on the trail, I am keeping both the iPhone and eTrex H in my arsenal for now. Besides, it's nice to have a backup GPS in my phone for redundancy. But if I left a device at home on a high-mileage trip, it would be the iPhone, not the eTrex H.