Memory Map are encrypting all (all?) their new maps. The QC3 format is encrypted and is locked to the installed app. The app itself is tied to the specific hardware. So this is a dead end for developers.
The QCT format was reverse engineered a few years back, has been documented, and now there are a few converters around. Whether anybody wants to develop a viewer for it, I don't know, given the limited map potential, with more or less the only maps being bootleg QCT ones, or scans of printed ones which somebody bothered to convert to QCT.
The much bigger GPS moving map app is Oxiexplorer which runs generic formats but (from postings on its user group) its author is very unlikely to drop everything and produce an Iphone version. And nobody is publishing copyright charts in generic formats because practically all maps in Europe are copyright and there is no money in publishing them in a generic format.
The Iphone 4 has a great screen; the best there is on a smartphone. Apps should make use of this.
The bottom line is that a GPS moving map app is a piece of cake to write, incl. one which would wipe the floor with MM. The trick is in the map data. You have only got to look at Jeppesen, whose Jeppview and Flitestar apps are really crap but all pros have to use them because of the data.
Some possible good news for Iphone users:
Development for other Operating Systems