As always ***SPOILER ALERT***
While re-watching "The Study in Pink," I noticed something. As Sherlock and Watson enter the restaurant at 22 Northumberland Street to wait for the murder, Sherlock greets the young man who opens the door for them. He calls him, "Billy."
Gatiss and Moffat have an encyclopedic knowledge of the Sherlock Holmes canon. There is no way they would pick a name for a random character who does not need to be acknowledged and given a name a name that matched a character from the canon. They deliberately gave the name "Billy" to an insignificant character in their first episode. Why? Maybe this insignificant character is not as insignificant as one might originally think. Maybe there is more to Sherlock's association with Billy than meets the eye. Maybe Billy has assisted Sherlock before they were both found in an opium den together.
Orrrrrrrrrrrrr.......Maybe not. Maybe they did put the name Billy in there intentionally, but only as a way to mess with the viewer, something I believe they would not hesitate to do.