For anyone wanting a fix for this add this to your NGG stylesheet:
.widget_slideshow h4 {
display:none;
}
The downside to this fix is that it is an ALL or NONE type of solution.. It removes the widget title for ALL NGG widgets.. For me this is not a big issue as I am using slideshows in my widgets and prefer to not display the title above any of them.. but for others, this may not be a fully satisfying solution..
Again I am running the LATEST version of NGG and despite the fact that this is reported FIXED in V1.5.1 - 23.03.2010, I can definitely report that this does not work for me in THREE separate installs of NGG.. Hence the need for me to find a workaround solution that doesn't get wiped out everytime I upgrade NGG as the fix below does.
Commented out line 29 as per this thread: http://wordpress.org/support/topic/plugin-nextgen-gallery-slideshow-widget-remove-sidebar-title?replies=5
nextgen-gallery/widgets/widgets.php
you have to remove the line
$title = apply_filters('widget_title', empty( $instance['title'] ) ? __('Slideshow', 'nggallery') : $instance['title']);
That does the trick. :-)