There is QT4 for the Nokia IT compiled now in the repos. You certainly could use QT, but as of now they are not integrated with the Maemo Hildonised look and feel. Nokia is in fact working on getting QT as another platform to work for the Internet tablets (with Meamo 5 maybe).

So might be good to learn up on QT. Aso another option would be to develop using PyQT - which is python bindings for QT. But PyQT is still not available for the Maemo platform.