I don't know if this has been pointed out (I didn't see it; I did check first!), or how relevant it may be, as, like the eBay thing, it could easily be a case of real-time circumstances, but in Fool Moon Harry mentions driving by Cook County Hospital:
"I drove past Cook County Hospital, a virtual city of its own inside Chicago," (Fool Moon, 39, paperback).
Cook Country was replaced in late 2002/early 2003 with the John H. Stroger, Jr. Hospital of Cook County, which Harry mentions in Small Favor:
"The Stroger building, the new hospital that has replaced the old Cook County complex as Chicago’s nerve center of medicine" (Small Favor, 392, hardcover).
I'd say this places Fool Moon pre-2003 (I am tempted to extrapolate on the fact that no mention of the construction adjacent to Cook County was made, but that's just me getting too caught up), and Small Favor after, possibly recently after.
Seems solid to me. When did the construction on the Stroger building begin? If
Fool Moon takes place in October of 2002, that only leaves one, maybe two months until it opens. OTOH, if it takes place in 2001, that leaves a full year and a bit.
Also, it just occured to me that the first chapters of
Grave Peril also take place at Cook, almost exactly a year later. this would seem to force the issue, dating
Grave Peril to 2002 and
Fool Moon, and consequently
Storm Front, to 2001 - literally, "The end of the twentieth century and the dawn of the new millennium".
Now, it could certainly be argued that the
Grave Peril reference is to the Stroger Hospital (
Wikipedia notes that it's also called "New Cook County Hospital"), but I do like the idea that the series starts out right on top of the 21st century, on purely personal grounds.
I'm tempted to combine that with the mention of "that pirate movie" (Small Favor, 77 hardcover), which is vague enough that it may or may not have been released in July 2003, and put Small Favor at the end of 2003. (Mind, there was another "pirates" movie that was released in 2005 that I can quite imagine Bob wanting to see, but I can't quite imagine it showing at a drive-in in Aurora, or Harry sitting through it with a pervy skull on the dashboard.)
The problem with this is that it compresses all the books between
Fool Moon (or
Grave Peril) and
Small Favor into one year (2003). This is clearly impossible, as numerous places in the books (referenced in the timeline) refer to months passing between each book - I believe the longest gap is between
Death Masks and
Blood Rites, which if I'm reading right seems to be more than a year and a half.
However, there was more than one "that pirate movie", the latest of which came out in 2007 and, assuming
Small Favor takes place in November 2009* (!), that leaves plenty of time for it to trickle down to the drive-in, which I assume probably isn't very high on the blockbuster distribution chain. Actually, by that logic, it could, in fact, be the first "pirate movie".
*The Timeline has it at the eighth year after
Storm Front.