Currently in SharePoint Beta 2, the option to save a site as a template is only available on the site collection. This is a known bug and is expected to be resolved in Beta 2 Tech Refresh build.
However, you can still save a sub-site as a site template by typing the explicit URL in your browser. All you need to do is append "/_layouts/savetmpl.aspx" to your site URL like this:
This will present you with the screen to save the site as a template.
Note: As I understand it, sites will not be able to be saved as a template if the Publishing feature has be enabled for that site. The publishing feature is available only with Microsoft Office SharePoint Server (MOSS) 2007.