One improvement idea: if user could type own coordinates in navigation screen - or change the current ones, that could be used when searching some mystery/multi caches with different coordinates than given in the description
I have had no problem with N9 built-in browser and gc.com.
Using AGTL as a base is really not an option since IMHO only using the real native tools (this time Qt & QML) is the valid if you want a real application instead of just some demo.