Mrs.Christie:Pottery Barn has larger floating shelves and I find the PB ones to be higher quality compared to the target ones. Regardless, if you are putting up long floating shelves you better hope your walls are true and straight (not bowing in or anything). I had several floating shelves on my walls and the larger 4 ft ones wouldn't hang right because my house was slapped together by contractors and consequently the walls bow in a bit in spots.
ugh good point. another reason maybe I should just be having someone do it for me. or find an alternative plan ;)