Cosplayisland, about the CE computer generated backgrounds. So far, looks like everybody voting for the usual greenbox technique, however I did just found an interesting image in CE "Behind The Scenes" section.
If You look closely, this is definetly NOT green background, although the guys on Cosplayisland may be right about the camera handling, as there are big crosses in the set - probably for the special camera, to record angles/distance. (As a hobby-photographer, I think they can't use green - green is good for movies, but looks ugly in photos, your skin will looks like a frog's...)
I'm not a big 3D guru (but somewhat familiar with Lightwave, Max and DazStudio), but my vote is: the backgorunds are made by Maya or Max, and they composite them with the girls via a special plugin.
In case You like behind the sceenes pics, here is another one with a nice pose:)