Many people expected something different from Google Sites and the name doesn't help the service too much. Google Wikis would have reflected the true intention of the service. "A wiki is a website designed for collaboration. Unlike a traditional website where pages can only be read, in a wiki everyone can edit, update and append pages with new information and without knowing HTML. Wikis are great for all types of collaboration, from writing documents and managing projects to creating intranets or extranets," explained JotSpot's intro tour.
Wikis created with Google Sites allow a very limited amount of customization and you can only embed content from trusted sources like YouTube or Google Docs. One of the causes for the lack of customization is that the wikis are hosted at google.com, instead of a separate domain like googlesites.com, and a script could easily compromise your Google account.