I do a lot of Shutterfly books. I use a lot of black backgrounds. I usually end up putting a white (or other light colored border) around each picture so help give the picture vs the background separation. I think it looks great.
My other Shutterfly tip, which you may already use, is don't upload all your picks into one album. I usually do 12x12 albums and they have over 100 photos in them. I do travel books so I will create a main folder then sub folders within each. Each subfolder is usually an activity. So when I'm working on my album I can just select the pics for a particular activity (album) and do those pages, then move on to selecting pics from the next activity. When I started Shutterfly it seemed so putzy as I was trying to sort though 100 photos at the bottom of my photo tab area which were small pics and I'd get so confused on which were for what thing. I also do the "hide used" option from the photo tab so I don't end up getting the prior activity photos included.