We expect to have this fixed for GA. Notes uses a number of helper applications and there is a bug where the OS believes that one of these child processes is the real applications and launches it the next time you try to run Notes.
For now, you can usually work around the problem by moving Notes out of the Applications folder temporarily and then move it back. This causes the Launch Services registry to get updated so it launches the correct process. Alternatively, you can run Notes from the command line using /Applications/Notes.app/Contents/MacOS/maclauncher.
Feedback response number CMAS7G7HYB created by Chris Majoros on 07/03/2008