In all, I found 10 states involved in nonclassified cloud-seeding programs.[3] Considering you can't find everything after only a few hours of searching the www, it stands to reason that there are probably still more nonclassified cloud-seeding activities around the nation.
Of course, based on the military's own information, it stands to reason that classified weather-modification activities are also happening. But the fact that widespread weather modification is occurring on an open basis means that witness accounts of activity fitting that profile are not necessarily significant. For me, these facts significantly reduce (but do not eliminate) the gravity of the mysterious-contrail case.
[1] Environmental News Service on mysterious spraying:
http://ens.lycos.com/ens/jan99/1999L-01-08-05.html
http://ens.lycos.com/ens/jan99/1999L-01-12-01.html
[2] Contains posts pertaining to the contrail case
including a claim that spray samples are jet fuel:
http://www.esotericworldnews.com/evenmore.htm
[3] Weather-Modification Programs In 10 States:
Nevada State Weather Modification Program: http://www.dri.edu/ASC/WxMod/HomePage.html
Oklahoma State Weather Modification Program: http://www.hpj.com/wsdocs/jul98/CR150645.HTM
North Dakota Weather Modification Project: http://www.swc.state.nd.us/ARB/html/ndcmp.html
A Cooperative Atmospheric Modification Program page (http://www.swc.state.nd.us/arb/html/noaamp.htm.html) says: "Presently [1998] six states are participating in the [NOAA weather modification] program: Arizona, Illinois, Nevada, North Dakota, Texas, and Utah."
California-based Weather Modification Project: http://www.dri.edu/Projects/Modeling/wxmod.html
A Colorado Weather Modification Program is cited: http://www.lubbockonline.com/news/100596/artifici.htm
New Mexico's "Llano Estacado Weather Modification program": http://www.cahe.nmsu.edu/pubs/resourcesmag/summer97/planting.html