Since I was seeing FireFox leaving temp files abandoned when the U3 version of Avast! is running, I was doing some tests of their free Home Edition on a host. When it is running (and the U3 is NOT), then StartPortableApps.exe crashes every time launched. The U3 Launcher and PStart work fine.
I'm not saying StartPortableApps.exe needs to CHANGE to accommodate Avast!, but there clearly seems to be a disconnect between Avast!'s program design & the evolution of USB drives which will come up again & again in support forums like this ... especially since any new Cruzer/U3 user is actively encouraged by U3 Software Central to install Avast! as a trial. I'll drop their support forum a note about these 2 issues.