I use them quite often on my layouts
Besides TV shows or movies, I am into Kpop and have also used stock photos of places or objects. I actually wrote a tiny rant about the use of them on my blog
For me, even if the photo isn't mine, the creativity and story (journaling) I put into my layout is
If it's possible, I always credit the photographer or website where I found my photos--I really like using sxc.hu, because you can contact the photographer directly there. Or I've also used vintage postcards I saw on flickr and contacted the photographer there
But um, I'm not going to use photos of babies that aren't mine nor things like fairies or gnomes. That's not my style.