Were Vietnam vets really spit on as much as is commonly believed?

This came up in a recent conversation. I've tried to include articles from both sides of the argument.

http://www.commondreams.org/views04/0318-12.htm
Myth Making and Spitting Images from Vietnam

http://www.wnd.com/news/article.asp?ARTICLE_ID=54165
Vietnam déjà vu (Revisionists deny spitting on troops)

http://www.rlg.org/en/page.php?Page_ID=95
The Spitting Image: Myth, Memory, and the Legacy of Vietnam

http://urbangrounds.com/2007/01/29/spitting-on-soldiers/
Spitting on Soldiers

http://www.thevoicenews.com/news/2003/0228/In_Response/R03_Bernard-re_Barlow.html
The Myth of the Spat-Upon Veteran By Gabrielle Bernard, Winsted

http://209.85.165.104/search?q=cache:Wwf1AUED4FUJ:newsbusters.org/node/10594+vietnam+spitting+troops&hl=en&ct=clnk&cd=30&gl=us
(Article is no longer available, but google has it cached.)
Resolving The Spitting Debate