I think that provided you aren't trying to make money off copying someone, then I don't have a problem with copying (or attempting to copy, recreate, etc) a design you have seen for use in your own home. I often find inspiration and, while I am a little bit creative, I don't have time to create truly original works of art at this time (though I'd love to in the future). That said, I personally never copy anything outright, I usually work some designs or ideas into my own thing. Where the line is drawn as far as inspiration vs copying, well, it depends on the project. Personally, I don't have the ability to copy wall decals in my home (apart from with paint!!) so it's usually that I would adopt a design and re-draw or re-paint it in a new way. Some things worth copying aren't available for sale (eg a design on the wall in a club, for instance) - but why shouldn't I appropriate it into my own home for my pleasure if I wish? Saying you shouldn't is being silly as far as I am concerned. Art is out there - bring it into your life and be better for it.
OK a little ranty there, but designers - if I love your stuff and it suits I'd love to buy it. If I have the money I will, but I won't always have the money!! If it even can be purchased of course! I will never attempt to profit by copying the designs of others though - phoar, the very idea leaves a bad taste in my mouth.
Of course the whole who is copying who debate ended up working in some designer's favour as I stumbled across some more cute wall decorations NOT being sold on Etsy (YET - hah jks, buy from the originals!).
These are from ferm Living in the USA. I love the tree wallpaper and the periodic table wall decals! That paper is hot... wondering where I can use it in my home.
[http://www.fermlivingshop.us/stickers/periodic-system.html]
[http://www.thewallstickercompany.com.au/content/product.php?itemid=214&page=4]
And the website featured in the AT post is The Wall Sticker Company - an Aussie outfit it seems. I love their stuff, especially the Baroque removable wallpaper available in any colour combo you wish - amazing!!
[http://www.thewallstickercompany.com.au/content/product.php?itemid=214&page=4]