The episode contains references to the season-wide story arcs of the first four series; the Abzorbaloff got his files on the Doctor from the Torchwood Archive (series 2), but the files on Rose have been corrupted by the Bad Wolf Virus (series 1). The newspaper the Abzorbaloff reads contains a reference to Mr. Saxon leading the election (series 3). Finally, the Abzorbaloff is from Clom, one of the missing planets from series 4.
Mr. Saxon reference: just before Elton sees the Absorbaloff's true form, he is reading a paper with a headline reading "Saxon leads polls with 64 percent." Albeit subtle, this is the first reference to the series 3 "Mr Saxon" arc keyword; prior to the series 3 debut, a "Vote Saxon" poster would also appear in Captain Jack Harkness (2007).
The Abzorbaloff was designed by a young boy named William Grantham. He had won a competition to design a Doctor Who monster run by the BBC children's TV program Blue Peter (1958) in 2005. William's prize was to visit the set of Doctor Who and see his design being brought to life.
Bad Wolf Reference: Mr Kennedy gives the LINDA members a picture Rose from Torchwood archives but there isn't any other information because of the "Bad Wolf Virus"
Victor Kennedy's mysterious theme sounds similar to The Master's theme when he was played by Roger Delgado. Whether this was intentional or not is unknown.