Follow includes two components: (1) a Mahalo toolbar (with the requisite links and search box) that also sports a dropdown of the Mahalo directory and buttons that let you say whether you would, would not, or might recommend the page you’re reading to a friend.
The second component (2) is the “Follow” aspect. Pop open the Follow sidebar (Ctrl+Shift+F), and Follow will provide you with Mahalo pages that are relevant to your interests, based on the pages you’re viewing. Don’t worry – it’s not logging the URLs you visit or anything, simply parsing for keywords and finding SeRPs that match. It’s most interesting when you’re searching on Google or Yahoo (or the others): if Mahalo has a SeRP (Search Engine Results Page) that matches what you searched for (say, “ipod” or “Minneapolis Bridge Collapse”), it will pop the sidebar open and show you that SeRP so you can judge whether the Mahalo page (with human-selected links) or the search engine page (computer-generated) is more helpful.