This issue went on sale two months late from the original shipping date of 659, one month late from when the actual content was to ship. This issue was originally supposed to contain a Krypto story, but Kurt Busiek announced first on the DC Message Boards on 2007-01-25 and later on the Newsarama Message Boards on 2007-02-11 that that (completed) issue was pulled at the last minute at the executive level to be rescheduled later, so this issue contains what was solicited for #660. This was confirmed by DC via a press release on the day the issue shipped, 2007-02-21.
Here's the solicitation text for the to-be-rescheduled issue: "Ever since the death of Superboy during the Infinite Crisis, fans have wondered what became of Krypto, and what those events meant for him. Now, writer Kurt Busiek is joined by sensational guest penciler Rick Leonardi (SUPERMAN RETURNS: LEX LUTHOR, BATGIRL, NIGHTWING) to tell a surprisingly touching tale of the Dog of Steel's most tragic days, laying the groundwork for Krypto's surprising future." (The solicited inks for this story were to be by Jesus Merino.)
The solicited issue (cover and story) was finally rescheduled more than four years later, and appeared as Superman (DC, 2006 series) #712 (August, 2011).