Amazing app! I downloaded my first map, with zoom 26. It has 92k tiles. I am using Froyo at an HTC Desire HD. My problem is: I can not do zoom out. I see at a scale of 90 meters. With the online maps I have not one.
You have to download more lower zoom levels, not only the highest (26?). Try (check the clickboxes) the download zoom levels 17,18,19,20.. to 26 if 26 is really neccessary.
You can test it by loading and creating a new small map with 3 lower levels (maybe) 17 18 19 an see how it works.
In addition to that, you can also use the "digital zoom". You find it in the lower panel.