Nikon updates that line range every 2 years...
D70 - 2004
D80 - Aug 2006
D90 - Aug 2008
If you follow that pattern, Aug 2010 will most likely be when Nikon releases the successor to the D90. It will likely be a Dx000 series although they might cop out and do a refresher (i.e. D90s or D90x).
"God's in His heaven. All's right with the world." - Robert Browning (1812-1889)