I recently did these layouts of my kids. As you can see I've used multiple photos. I think this is a great way to save on your scrapbooking. Let's face it if I did one layout per photo I'd use alot more supplies than I have here. I love to use multiple photos whenever I can. I really only do a single photo per layout when I'm wanting to produce something of the same artistic value as the layouts featured in the magazines. I also tend to resize alot of the pictures on a common theme and print them on one single photo. (See example) I then cut these out later, and use them on my layouts. This is especially useful if you're scrapping an event such as a wedding or birthday party. This montage of photo's is from my son's birthday and was printed on a standard 5' x 7' photo.
This evening I found a great blog which shows lots of examples of multiple photo layouts. So if you're wanting to try this technique, or just looking for new inspiration go to: http://scrapbooklayouts.blogspot.com