I learned something new tonight. Or re-learned; maybe I'd forgotten. Ravelry has a wiki... and there are errata within! For example, there is a link to corrections for Cat Bordhi's New Pathways For Sock Knitters, Book One in the book errata page. (Yikes, there is a correction for the master math I just went through!)
The Ravelry wiki has many lists of links to useful information on the web.
Right now, in beta, Ravelry's search facilities are limited, but I'm assuming that will improve with time. Eventually you should be able to search Ravelry like you can search the web with Google. I haven't seen any promises, but it's a pretty obvious requirement.