Hmm.
Now when extras is enabled out of box in N900 it means that QA should interest Nokia also. End users do not understand where programs come. They only see that device is from Nokia and programs come also from Nokia. And if quality is not perfect then they blame Nokia.

So I´m not sure if Nokia should enable it by default. Maybe disable and give user option to enable it with warning and when installing stuff then also warning that Nokia doesn´t give any support or promises that programs work.

Currently for example widgets/im protocols and programs that install daemon to background seem to be high risk programs that should undergo much much stricter QA than single app or theme.*

*One way to decrease incompatibility of new fw and apps in extras is to release devel fw. And this seems to be case with Meego?

.edit
gqil's idea about promoting good apps to official Nokia channels sounds good to me.