Another nice feature of the YouTube Video Editor is adding photos. While you could use it for importing a slideshow of photos, I use it for the title page on all of my videos.
As far as the slideshow, importing the photos works well enough, but the "copyright free" music is on the lame side. YouTube needs to either get rid of the audio section entirely, or come up with a way for users to use licensed music for their creations.
As for the title page I think inserting a photo works great. There are features such as auto-fix, brightness, and pan & zoom that give a nice animation feel with little expertise from the user.