Again,
http://www.soaw.org has a lot of information about the vigil and why the organizers are putting on the event. Here's a link to a report from last year's event:
http://www.soaw.org/new/article.php?id=1013
I was there last year, and it was a very powerful experience. There were a few signs related to other issues (Iraq, Palestine, etc), but the focus was really on SOA/WHINSEC/Latin America.
Saturday has the rally with a number of speakers, and Susan Sarandon, Sr. Helen Prejean, Amy Ray, and a number of others were there. In late afternoon, there's the puppetista parade, which was impressive. Sunday morning was really moving. They had the "Presente" ceremony where the leaders chant the names of those killed by SOA grads and their ages. The crowd responds to each by lifting their crosses and saying, "Presente" ("I am here.") It lasted a long time because of the sheer number of victims, and it was especially wrenching when they were just babies.
The people there are generally a little more subdued than the stereotypical protester. There are a number of nuns, priests, and other religious leaders there, and there's a wide variety of ages.
Except for the people who decide to "cross", there aren't many arrests, since it's quite peaceful.
There are a couple of videos of speakers up at
http://www.archive.org (just search for SOA). Sr. Dianna Ortiz is an Ursuline nun who survived torture (which SOA grads were linked to). Her speech is at
http://www.archive.org/details/ortiz . Peg Morton is an activist who went to prison for "crossing the line" at an SOA vigil.
http://www.archive.org/details/soa-qt-sorenson-40-perc