OK I am a bit confused (nothing unusual about that).
PR 1.2 will give us full QT support.
But does that mean that all previous programs written for the N900 will need to be ported via QT or will they still run as normal?
Does this mean that all programs currently shipped with the N900 will be updated when PR1.2 comes out?

If I modify a current program on the N900 will it get changed during the update?

Your old programs will continue to work.
Some programs might get ported over time to make them also run on MeeGo and Symbian.

When will we see some tutorials for qt + maemo or meego? So far there isnt anything around.

Qt (not QT) support is improved. This does not mean that it replaces anything - except older Qt.

Qt in itself only expands on the potential and life lenght of the N900. Software made for Qt on the N9 will also work on Qt on the N900. More or less.

On the other hand, since Qt is considered the future, some people want to remake their software in Qt. This means that instead of spending time improving their lovely N900 software, they're sitting on the fence, considering if they should start over in Qt. IMO, the N900 biosystem took some (considerable) short term damage from this, but the life cycle can extend a bit longer from it since it's more compatible with other biosystems.

Bluetalk: I would expect that we won't see any tutorials for Qt + Maemo 6 until there exists GUI guidelines for Maemo 6. At the moment there is no UX.