From the SMX East 2008 search marketing conference, this is the "What Is Spam" session involving Google, Microsoft and Yahoo. Presentations, in order of appearance:
Nathan Buggia of Live Search covering what search spam is, search engine guidelines against spam and specific reinclusion tips for Microsoft's Live Search.
Aaron D'Souza of Google giving an overview of what "on page" spamming is, such as keyword stuffing, hidden text and cloaking. He also offers specific reinclusion tips for Google.
Sean Suchter of Yahoo providing an overview of issues about link spam and paid links. He also covers specific reinclusion tips for Yahoo.
Q&A for about 30 minutes follows the presentation.