Allow the selection of more than one image in the slideshow for Create Background Slideshow

Being able to select and alter the timings of more than one one image at once would make changes to imported slideshows much easier.

Introduce a method to copy the duration to the transition for Create Background Slideshow

For constantly transitioning slideshows, such as the All-Day Wallpaper, it would easier if the transition automatically used the duration value, or there was a button that quickly copied the value across.

Pare down the main GUI for Create Background Slideshow

Reduce the clutter of the main window. Move toolbar to top. Scrap notebook in favour of an iconic switcher button for Defaults/Selected. Only have duration and transition, in drop-downs. Move other options to a separate Preferences dialog.

Use comboboxes to select the timings for Create Background Slideshow

Comboboxes can contain a few "typical" timings, as well as "Default"/"Auto" and a custom timing. Follow the combobox with an "Edit" button to change the custom timing, which will pop up a few widgets for selecting the new duration/transition along with an OK button.

Adjust image durations automatically to fit a given slideshow length for Create Background Slideshow

Add a 'slideshow length' selector, coupled to a checkbox that selects to adjust the default duration of images so that the total duration of the slideshow matches the chosen length. Based on the first comment at gnome-look.org, from TheWiseDj http://gnome-look.org/content/show.php?content=125710