Every time I want to import pictures into f-spot, after clicking "import" and chosing a folder or device I need to wait for thumbnails of all pictures in the chosen folder/device to load before I can start the import. Also, every time I check/uncheck one of the options below, f-spot starts loading thumbnails anew.

Possible improvement: 
1. Show a standard symbol in place of every picture in the selected folder.
2. Load thumbnails in background and progressively replace standard symbols.
3. Allow the user to select pictures and start the import without waiting for the thumbnails to finish loading. Especially if you want to simply import the whole folder this would save you a lot of time.
4. When options below are changed, apply changes to the preview window, if any, without reloading every picture.