Until recently, Google required people to follow several erroneous verification steps if they wanted to sign up for a Google Account using their existing email address, such as a @yahoo.com, @hotmail.com, or other address. Google has now simplified the sign-up process for Yahoo! users.
To make this process simpler, Google is now using OpenID, an internet standard, which is supported by several email providers, including Yahoo!. Instead of the process above, Yahoo! users who sign up with Google see the page above with a button that sends them to Yahoo! for verification.
Once you click that button, Yahoo! shows you a page to get your consent to share your email address with Google. After you agree, you’re done and can start using any Google service, such as Google Groups, Docs, Reader, AdWords, etc. In the future we hope to expand this feature to other email providers, and we also hope other website operators will read more on the Google Code Blog about how they can implement a similar feature. We are always down for anything that simplifies tedious registration processes. Check out the official announcement on the Official Google Blog.