I tried out plugandpaint example and everything works fine.
Did you output some debug messages in MainWindow::loadPlugins() (don't forget CONFIG +=console)?
Do you use VS2005 -> did you also copy the .manifest files?
Take a look into the registry (regedit) under HKCU\Software\Trolltech\Qt Plugin Cache 4.2\ (or Qt Plugin Cache 4.2.debug for debug) to see if your plugins are found and if they've the correct build key.
The plugandpaint example loads the plugins manually so it should be easy to see if they're found by modifiyng MainWindow::loadPlugins().
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