Just upgraded from 2.9.2 to 3.01. I've been happily running 0.2.1. using the widget to display posts which I've tagged "featured".
When I upgraded, the featured posts were still appearing fine. However, I was prompted to upgrade to Query Post 0.3.1, which I did automatically. Despite all of the reassuring messages after the auto upgrade, the widget stopped working, displaying only a small, empty, partial box.
I restored 0.2.1 manually by deleting 0.3.1, and then copying back the old query posts directy. It works fine.
I confess I didn't spend much time with 0.3.1 trying to make it work. I did not spend any time checking out the widget, for example. However, I assumed it just ought to work.