I thought the toolbar to be a little bit confusing.

I often click on the open button instead of the import one an audio/video element.

Since user is not supposed to click create a new project or to open another project many times while using PiTiVi, i suggest to let these functionalities in the menu bar and to keep in the toolbar the tools that the user may often use : 
Import clips | render project | Fullscreen

For the same reason, Save and Save as buttons are not necessary : Save as may not be used very ofter and, concerning Save, i expect PitiVi to be smart and to automatically save my work