For keeping Yahoo! up-to-date report to Yahoo! either of the following:

• links that results in an error message
• links that are dead ("Not Found," "Doesn't Exist," etc.)

Here is the dead link reporting URL: http://docs.yahoo.com/docs/writeus/deadlink.html.

You can also report if member is abusing Yahoo! services. Here is the URL:
http://add.yahoo.com/fast/help/abuse/cgi_abuse

You can remove own Yahoo! accounts and its information from Yahoo! at any time. By terminating your account, you will lose access to your Yahoo! ID, Yahoo! Mail, and profile names. Yahoo! will also delete your account data and settings across the Yahoo! network and it takes minimum 90 days.

For remove your entire account, please visit at https://edit.yahoo.com/config/delete_user. You will be asked to sign in to or verify your password for the account you wish to delete.

Google

Do you want to send a reinclusion request to Google? This has changed in the last few months from an email address to a web form and the best location is http://www.google.com/support/bin/request.py. You can select “I’m a webmaster inquiring about my website” and then select “Why my site disappeared from the search results or dropped in ranking.” Click Continue, and on the page that shows up, make sure to type “Reinclusion Request” in the Subject: line of the resulting form. Upper- or lower-case doesn’t matter, but make sure you use the words “reinclusion request” in the subject line so it gets routed to the right place.

In Google the best place reporting SPAM is to go to http://www.google.com/contact/spamreport.html.