If you haven't updated to Windows 7 Service Pack 1 (SP1) yet, you'll be forced to in the coming days. Microsoft are rolling out SP1 automatically through Windows Update, so you'll no longer have the option to opt-out of the update.
Previously, SP1 was available on Windows Update, but required the user to action the installation. As of tomorrow, the installation of SP1 will be fully automatic, not requiring the user to choose to update to SP1 or not to those who have Automatic Update enabled. SP1 will eventually roll out to all customers on the RTM version of Windows 7.