Unless you want to write incompatible per platform (Dalvik, objC, .NET, Enyo/Mojo,...) app always all over again, Maemo & company are still the best bet IMO. You can quite easily use or port standard Linux libraries and use standard GUI toolkits. Running the same mobile application on the desktop during testing is also easy & very handy.

I'm not saying making a truly multiplatform mobile application is not doable, just hard - I have quite a few ports in progress already.