The a-gps of the iPad2 uses a 3G connection to provide the almanac for the gps engine. It also uses 3G tower triangulation as some sort of aid, but I have been unable to find any real detail on how this works. The almanac lookup function is normally on board the gps engine. So, if the iPad has moved significantly since it as last used and there is no 3G coverage, it can really struggle to get a fix. This can be probably addressed with a bluetooth gps engine, but I haven't yet tried this.
The bit that concerns me us that ozrunways does not reliably give an alert that the gps signal is inadequate. This may be a shortcoming of the iPad2 more than ozrunways, but it's real. Ozrunways is a good thing and the average Vfr pilot will find it good, especially on local flights. But it's lack of loss of integrity warning is a concern for IFR use where there are less options to cross reference the validity of the location information. I have enough screen shots of patently wrong location data despite " green" gps indication to be sure about this.
There is another issue about GPS speed. Apple don't disclose the refresh rate of the iPad. It's probably 1 Hz. But the thing about the common consumer gps engines is that while they are advertised as 1 Hz, few really are. The limiting factor is processing speed. If the engine is still finishing the calc on the previous position fix, it will skip th next. Typically 1 Hz gps engines skip 1
pr 2 out of every 5 readings. GPS engines typically take 800 m sec to do the calc and output the data. 5 Hz, 10 & 20 Hz engines are dramatically better ( and significantly more expensive which is why they generally don't feature on consumer machines). I would really like to see a 5 Hz engine ( as s used on Garmin aviation GPS units). I haven't yet found one thats Bluetooth, but Gamin do nice USB & serial ones.