evaristo: The newest version of the script does what you want. It is a little cludgy since it moves around the view a bit, but it works.

re: evaristo
That shouldn't be a problem. I will implement soon.

re: #000000hA7
1) there is no mouse wheel on a laptop or on most macs
2) this script had shortcomings when it comes to list view

Great script. I use list view to read items though and the current script pops open items to mark them as read.

I used a bit of this code to create a new script which will mark items as read without opening them first:
http://userscripts.org/scripts/show/25522