Portability is a myth. (and nice buzz-word for marketoids)

You have two options using "portable" libraries:
1. Use platform specific features - thus rendering your application unportable
2. Use lowest common denominator - which prevents you from creating truly awesome apps

P.S. I've been working on Psi Jabber Client which tried the third way and wanted to reimplement platform specific features for every platform. Foreseeable - it failed miserably.