There is really no set pattern and worse, Disney is now bucking any historical trends by raising different tickets at different times rather than raising everything at once. Recent history shows:
March 2004 - PH/PHP's (Gate & Advance), AP/PAP's, FL Seasonal
February 2004 - UPH's (Gate & Advance)
June 2003 - all gate prices except AP/PAP (No advance prices changed)
September 2002 - across the board
January 2001 - across the board
I wouldn't expect another one until sometime in 2005 but two increases in a span of 8 or 9 months is not unheard of.