Not to rehash an old story, but if you look on Delta Airlines website under allowed electronic devices (at crusing alt) it lists GPS devices as allowed.
Note that even if applications like this existed, they wouldn't exactly be legal to use as a primary navigation source for the airplane. The applications wouldn't be certified for flight usage (theoretically it's possible to certify them), but, the Droid hardware definitely is not.
In short, any information provided would have to be an information only kind of thing, and you would need to verify everything with the existing avionics and/or instruments that are in the plane anyway.
@rotordroid: i think the weight and balance app is a great idea as well. i'm studying to be an A&P mechanic right now and we do plenty of weight and balance calculations
Someone might make an app, of course until then you could use GM with topo, but ... I have a 430 in the console, and a 496 on the cyclic mount, haven't yet really needed it on my droid hehehe.
The new Garmin AV8OR tablet-sized and handheld-sized versions are IFR certified up to non-precision approaches. They also only cost about $1000/$2000 respectively and can do things like play music and videos, or convert to an auto GPS database when you're on the ground. You can hook it up to (XM I believe) satellite weather antennas to get realtime weather overlay.
It's a must-have for any VFR pilot, in my opinion.
The Droid, on the other hand, is nowhere near accurate or stable enough to use as an avionics system. You *might* be able to get away with using the compass as an HSI.
Av8or is Bendix, newest Garmin portable is the 696 tablet, while it can satisfy the electronic chart requirements, neither are approach certified.
Can you post a link to the ones you are speaking about?