* As part of the setting update, the men who would have been almost exclusively called Holmes and Watson in their original incarnations are now called Sherlock and John.
* Mrs. Hudson's neighbour's name, Mrs. Turner, is a particularly obscure reference to Scandal in Bohemia.
* There's a brief shot in 221b Baker Street of Sherlock pinning some papers to the mantelpiece with a small knife. In the books this is exactly how Holmes keeps his unanswered correspondences.
* "Domestic bliss must suit you Molly, you've put on another three pounds since I last saw you." "Two and a half." "No, three." From a Scandal in Bohemia (though it's Watson, and seven and a half pounds).
* Sherlock repeatedly refers to the Czech Republic by the anachronistic name "Bohemia", just to make sure we get the reference.
* "Any ideas?" "Seven, so far..." From The Adventure of the Copper Beeches.
* The Science of Detection website includes a dummy archive of Holmes's past cases, which all have intriguing titles (some of them referencing Watson's untold stories from the canon, such as Isadora Persano and the worm unknown to science, or "the dreadful business of the Abernetty family").
И это не считая того, что вполне очевидно для любого читателя Канона.
Upd: см также: http://community.livejournal.com/sherlock_series/16138.html