Strange(?) Opera Floating

Answer 1

Are you using any css reset code? Off the top of my head it seems like you're getting extra padding on some of your basic elements.

Just for kicks and giggles, try removing the padding and margins on all of your elements inside dataGroup, before setting them manually.

.dataGroup *
{
    margin: 0px;
    padding: 0px;
}
...
.dataRow...

Answer 2

If you use the pseudo selector :after, like so :

.dataRow:after 
{      
    content: ".";  
    display: block;  
    height: 0;  
    clear: both;  
    visibility: hidden;
}

That should fix Opera, and of the top of my head, I believe IE8 also supports :after.

Shamelessly borrowed from Position is everything