Who would have thought? Indoors we use them to create an illusion of spaciousness, provide an interesting focal point to an otherwise empty wall, reflect light, and highlight more visually pleasing views. So why not bring the magic outdoors?
Like indoor mirrors, outdoor mirrors add interest and lend a view where there might not otherwise be one.
Hung in a screened porch or patio area they make the space seem more like an extension of the home's indoors: 
In a garden, they provide more light to shady areas:
We love the whimsical, romantic vibe of this secret garden window mirror:
Picking decorative mirrors with that mimic their environs can make them seem more fitting to the space:
(Images: 1: My Home Ideas via the inspired room, 2: Traditional Home, 3: HGTV via Holly Christian, 4: Primrose London, 5: Ballard Designs)


Howard Butcher Bloc...
Ooh, I really like this effect!
LOVE.
I adore this look and did something similar as the third picture, it was the same shape/stype only it was a black frmaed mirror on a fence and EVERYONE who saw it made crack about "why is there a mirror there?" So if you try it, be prepared for friends and family NOT to get it. I think I left it when we sold the house; I should see if the new owners got rid of it :-(
my mom does this! i wish i had a picture. her front patio has a few mirrors scattered about, and i've always liked the effect. ec05 - trust your instincts and ignore the (clearly unstylish) friends and family :)
Crappiest photos ever! What's the deal with all those pixels being so huge and whatnot.
I picked up a mirror in my alleyway just a few days ago, to do this same thing! Unfortunately, it's really big, and frameless, so now I'm not sure how to mount it to the trellis that I had thought would be a great place for it. Hmmm...
= A whole lotta dead birds.
I've been using mirrors outdoors for many years....I even keep one on a table top with flowers sitting on it...I enjoy seeing the trees & sky reflected on my table top & who cares if no one "gets it", right?
Really gorgeous idea! I would love to try it, but also afraid that no one around our small town home would "get it." We have a funky home and interesting decor and no one gets that either! I finally found an eames lounger to bring home and multiple people have been saying, "ugh that thing is ugly." I love it, so too bad for them! :) I do want a mirror in our backyard though!
http://www.makemineeclectic.wordpress.com
Never thought of that. Gorgeous.
Our house came with those in the backyard. I really dig them but the dogs still periodically get confused by them.
I have three in my small urban yard. Reflects the vignettes that are extra special such as a bench of bonsai trees and a special seat grouping
Jessie Marie33, don't worry what others may be doing. Go funky and trust your instinct and inner style
I really like the blue window mirror. I can't figure out how it is done with it looked like it is opening up. Can someone tell me how? Thanks