After a few delays, the PR 1.2 firmware for the N900 is finally released with Qt 4.6.2 shipping by default (see maemo.org for all PR 1.2 related info). This means that all the apps that up until now only ran in the SDK can finally be deployed to real devices :)
The final Qt packages have the version tag 4.6.2~git20100401-0maemo1+0m5 (no April Fool's, despite the date).
Some useful information:
A good starting point for developing with Qt for Maemo 5 is the Nokia Qt SDK.