Oh my God, twitter bootstrap is a pretty damn good styling and widget framework. Check it out!
My first issue with it however is that I couldn't find a way to change the tooltip label after it's been created.
It's easily solved, but with a rather convoluted and hidden method.
$('#target').attr('data-original-title', item.value + ' selected.').tooltip('fixTitle');
What this one line wonder does is change the title attribute, then tell it to update using the "fixTitle" call.