I somewhat agree with Billy about 2001, though I would argue the mental decline actually started right around '96 with the change to the generation doctrine, and solidified at the turn of the century. It took a few more years for that reality to fully set in, as people realized that the "end" was basically open-ended now, there was no immediate goal to look to on the horizon, and the zeal was all but sapped out of the WTS.
If you look at the growth numbers, it backs that up. Growth in the early 90s was always between 4.5-6%, with the trend line slowly dropping as you approach 1994 (80 years from 1914, i.e., the lifespan of a humany being "80 years in case of special mightiness" that a lot of people were clinging on). Bit of an uptick in '95, but before the generation change comes into play. Then the generation change happens. 1996 growth drops by one whole point which was the biggest single year drop in a while. It goes into freefall after that, with a huge 1.6 point drop between 98 and 99, which happens to correspond to when the internet started getting mainstream.
It finally hits 1.7% in 2001. Another uptick in 2002 to 2.8%, which is most likely because of 9/11 getting some formerly inactive JW's (and the public at large's) fears up. 2005, cedar's year in question, was a new low at 1.3%.