Just been trying it out I prefer it to Fox Tab, to add an image you edit the group > Additional Style Options.
If you don't want the image to tile you'll have to make it large enough to fit your maximized browser window. Its pretty versatile advantages over Opera's Speed Dial
You can have several pages tabbed in groups.
You can add a custom image to a tab easily ( possible in Opera as well but harder)
You can Crop a thumbnail to show the site's logo & you have precise control.
Thumbnails always stay in the same spatial relationship Opera 11.10 beta Speed Dial Advantages
No empty thumbnails just keep adding by the + button & you set the size of the thumbnails by the zoom.
Scroll bar shows when you have lots of thumbnails or you resize the browser window smaller.
Default behavior is auto cropping of thumbnails to Site's logo ( no fine control can only set thumbnail to reload & it will show all the page.)
Can easily drag a tab to a thumbnail by dragging with right mouse button to a thumbnail or + button press shift before you drop
You Can Synch your Speed Dial Thumbnails
Firefox Speed Dial is impressive once you learn how to set it up.