My system was stable before installing this upgrade. Since then, I have had a series of crashes - mostly in Apple's own apps! They seem particularly to affect commands in the File menu - printing is especially dodgy. If I attempt to print to a shared printer whose host machine is asleep, the app will certainly crash. Often it crashes even if the machine is awake! Saving often causes a crash as well. Both Final Vinyl and CD Spin Doctor have become unusable since the upgrade, although Audacity seems to work fine (even the apparantly unstable v1.3.0b!).
I can't prove that QT 7.1 has caused all of this - but it didn't happen before the upgrade and the problem seems to be system-wide!