I see a lot of accidental silhouettes on Facebook. In another post, I write about the importance of taking 5-10 seconds to really SEE your background before you take a picture. Whether shooting with your phone or a fancy dslr, a brightly lit background is going to confuse your camera sensor, the best of which is no match for the human eye.
If you don’t want your subject to appear as a dark blob in front of a magnificent Bryce Canyon vista on your once-in-a-lifetime vacation, turn on the flash! Most digital cameras do a pretty good job of balancing flash and ambient light. With a little practice, you can do it really well.
Of course, if you want a silhouette, which can be a very beautiful effect, you can get one with very little exposure effort. The trick with silhouettes is to ensure the subject is recognizable by its shape.
Another option for backlit scenarios is to expose for the subject and blow out the background. I guess this choice depends on how you feel about the background.
So, in a backlit situation you can add light to the subject to balance with the backlight, expose for the subject and let the highlights fall where they may, or expose for the background and make a silhouette. Hey, you’re shooting digital, so why not try all three when you get the chance?