Kent Boogaart has created his own BooleanToVisibilityConverter that addresses some requirements of the original one.
Source: Kent's Blog
This is a small thing, really, but how often do you curse WPF's BooleanToVisibilityConverter (or Silverlight’s lack thereof) because it doesn't allow you to convert true to Visibility.Collapsed instead of Visibility.Visible? Or what about converting false to Visibility.Hidden instead of Visibility.Collapsed?