I filed enhancement request 1324 to add a mouse double-click test area (http://bugs.pearsoncomputing.net/show_bug.cgi?id=1324).

If you read the request you'll find a link to a screen shot of such a feature in GNOME:

http://www.bbc.co.uk/accessibility/guides/mouse_easier/doubleclick/linux/gnome/index.shtml

If you are familiar with GNOME perhaps you could help track the code for that dialog and provide some links here or in the bug report.

Thank you!

Darrell