A link sent to me by Teresa has come just at the time I was thinking how to make a bit of a windbreak that will not block the sun on that side. Although I do not drink soft drinks (except for Tonic in my gin!) I could probably gather enough from others to do this. There is no container deposit here in Tasmania, which is shocking but true!!
Like Pattie, I do worry about the leaching of nasty things from these bottles into the soil and water but I wonder if plants would take them up.... I'd say probably not, although I don't really know.
This would be a fun thing to do at a community garden too and could be used around a play area, for example. Probably best at times other than mid summer, but maybe here in Tasmania it might be ok.
The whole preparation process is fully explained on this Container Gardening blog.