Here's an idea that some folks may not have considered, if you want the grouped view style but find those rounded corners just too '2008', create a transparent PNG, create a row with minimum height (1, not 0), i.e.

var blankRow = Ti.UI.createTableViewRow({height:1,className:'blank',backgroundImage:'images/transparent.png'});

and insert it in the top and bottom of your sections.

Obvious really.

cheers,
Chris.