This is a really interesting question, lm44west! I use scrapbooking as a way of getting our family's memories recorded in a tangible form for the kids, grandkids, and eventual multiple-greats to read. So for that reason, I tend to stick with photographs I've captured. I have so many, and I'm so far behind in scrapping them, I think I'll never run out!
However, sometimes there are layouts I want to create for which I don't have images, and for those, I'll hit up a Google image search. Like layouts about current events, I'll grab shots from news sites, or anything about pop culture, I might grab movie posters or album covers or that kind of thing.