The GUID is the new identifier for the user's profile on profiles.yahoo.com (and currently for many properties on Yahoo!). Depending on what you're actually doing for your app, and what properties you're accessing, you may be able to use the GUID and
YQL to capture the data that you want. If you have more details about what you're trying to do we may be able to assist to get you up and running.
Jonathan LeBlanc
Senior Software Engineer
Yahoo! Developer Network
thanks for your reply,
Finally is there any other options to get user yahoo id with out asking him,
I need to take his yahoo id as a user id for my app.
I think guid is nothing for me,i had all the user infomation with out their yahoo id what is the use of this information