While it is a joyous occasion, the Nexus One update to Android 2.3.3 Gingerbread is not without its faults. Some users are reporting that after updating, Google Voice is broken. A few industrious souls have found a way to correct the problem easily enough, even if it is a bit more hassle then if, well, the update hadn’t broken GV in the first place.
If the problem is affecting you, simply uninstall Google Voice, locate, download, and install and older version of the APK, and then upgrade to the newest version via the Android Market per usual. Or sit around and wait for Google to issue a fix. What ever floats your boat.