When the keyword is (not set) it could be:

-- Direct traffic, where the visitor typed a URL in the address bar, or had previously bookmarked the site in his browser, or clicked a link in an non-web email

-- Referral traffic, where the visitor clicked a link on a page on a different site that pointed to your site

-- From a cell phone, and you can tell because the screen resolution is small, like for example 320x396. But I think whenever these show up as keyword not set, they also show up as source = Direct. If someone on a cell phone uses google to search, you see the actual keyword.

-- Patey