Reminder: remove Google search history before new privacy policy
google.com
google.com
So at the moment your search history isn't associated with your Gmail account, your YouTube account, etc. but if you leave it there until after this change it will be associated with your account identity.
This is a last chance to remove your web search history (my account had over 15k+ searches) before it is associated with your real identity.
If you prefer getting the benefits of better recommendations based on your usage history, then leave it - that is the only major downside. If you are not comfortable with all of Google knowing your search history, then delete it.
More information from EFF: https://www.eff.org/deeplinks/2012/02/how-remove-your-google...
[UPDATE 2/22/2012]: Note that disabling Web History in your Google account will not prevent Google from gathering and storing this information and using it for internal purposes. It also does not change the fact that any information gathered and stored by Google could be sought by law enforcement.
Take a look at the privacy policy for details on when your information actually goes away. (It's not overnight, but Google does make sure that the information really goes away: even from tape backups.)
I believe this is happening a week from now (and the EFF article is still linked on the front page).