This issue had a different cover and first story than what had been originally solicited (the solicited cover and story ended up in Superman #670). This change was announced by a press release on 2007-09-18.
There is an inscription "TO NEAL ADAMS AND H.P.", the cover is an homage to Superman (DC, 1939 series) #233 by Adams and referring to H.P. Lovecraft's Cthulhu.
Story continued from Superman (DC, 2006 series) #667. In promotional materials, this is called part 2 of the 2-part finale of "Camelot Falls", and was originally scheduled for Superman #668. In the panel where Superman stops the tidal wave (page 17), Carlos added "TO ROSS AND TERRY" on the panel border. On Geoff Johns' message board on 2007-12-01, some fans mention (and Kurt confirms) that that is a reference to Ross Andru and Terry Austin's work on the first Superman vs. Spider-Man crossover, which had a similar scene. On the DC Message Boards on 2007-10-02 and the next day, Kurt talks about the art, saying that Merino is sharing the pencils with Pacheco, and "doing quite a bit more than layouts, but not full pencils."
Terabithia is likely a reference to the "Bridge to Terabithia" book/movies, but could also be a reference to an island in "Prince Caspian" and "The Voyage of the Dawn Treader" by C. S. Lewis called Terebinthia. Per Kurt (in a question and answer session on Superman Homepage on 2007-12-04), the reference to Kara being from Kandor is a mistake; it should be Argo.