Philipp Lenssen reports that a bug in the Google Toolbar warns users when they select other search engines to use. If you enable in the toolbar that you want to keep Google as your main search engine, and you install a toolbar from say MSN, it will pop up warnings at you. The warning reads, "Google has blocked an attempt by another program to change your default search settings."
Benjamin Lewis from Google said there is a bug with the program, "The fact that GoogleToolbarNotifier.exe remains in memory after disabling the feature is a bug – thank you for reporting it. We're working on it right now and should have it fixed shortly. As long as the feature is disabled the .exe doesn't actually do anything, it just remains in memory (not that this makes it less of a problem)." More details at Google System blog.